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Types of Nuts: Hex, Nyloc, Wing, Flange & More Explained
When this article says "nuts," it means fastener nuts — the threaded components that pair with bolts, studs, and threaded rod to clamp assemblies together. There are more types than most people realise, and choosing the wrong one costs time, causes failures, and occasionally causes injury. This guide covers every nut type you will encounter in Australian trade and industrial work: what each one is, how it works, when to use it, and what class to specify for the bolt you are pairing it with. Bookmark our Engineering Reference Charts hub for related sizing tables, conversion charts and Australian standard references across 9 topic clusters. What Is a Nut and How Does It Work? A nut is an internally threaded fastener that mates with an externally threaded bolt, screw, or stud. When tightened, the nut bears against the surface of the clamped material on one side while the bolt head bears against the other. The act of tightening stretches the bolt very slightly — this elastic elongation (bolt tension, or preload) is what creates the clamping force that holds the joint together. Friction between the bearing faces and the bolt-thread/nut-thread interface resists loosening under normal service loads. The thread form defines geometry: metric nuts follow the ISO thread standard (60° thread angle, pitch in mm); imperial nuts follow either Unified National (UN, 60°) or Whitworth (BSW, 55°) standards. Metric and imperial threads are not interchangeable — forcing an imperial nut onto a metric bolt (or vice versa) at a nominally similar diameter will damage threads or give a false sense of security on a mismatched pair. Thread engagement length matters. A nut that is too thin may strip before developing the bolt's full proof load. This is why thin nuts (half nuts, jam nuts) are not direct substitutes for standard-height hex nuts in structural applications. The standard height for a metric hex nut is approximately 0.8 times the nominal bolt diameter — enough engagement to develop the bolt's rated proof load without stripping the nut threads. For tightening nuts on hex bolts, open-end, ring, and combination spanners are the standard tools — our Types of Spanners guide covers selection and sizing. For production work and accessible bolting, a socket set driven by a ratchet or impact driver is faster. For critical applications with a specified torque, a torque wrench is required. The nut drives the bolt tension, and the torque applied determines the resulting preload — both under-torquing (loose joint) and over-torquing (yielded bolt) are failure modes. Hex Nut (Full Nut) The hex nut — also called a "full nut" in Australian trade — is the baseline. Six flat faces accept a spanner or socket, the standard internal thread height develops full engagement with the paired bolt, and nothing else about the design is optimised for anything in particular. It is the correct choice for any application where a specific nut feature (locking, capping, extension, quick-release) is not required. In Australia, hex nuts to metric dimensions follow AS 1112.1 and are specified by property class: Class 5, 6, 8, 10, or 12. The most common stocked class is Class 6, which pairs with 6.8 and 8.8 grade bolts across the majority of general industrial and construction applications. Class 8 hex nuts are specified for high-tensile 8.8 and 10.9 bolt assemblies where the nut must develop the full proof load of the bolt. (The nut-to-bolt matching rules are covered in detail in the Property Classes section below.) Hex nuts are available in standard and wide-series (larger across-flats dimension for greater bearing area), and in normal and thin (half-nut) heights. Standard-height hex nuts are stamped on the bearing face or across the flats with the property class number. A hex nut with no markings is generally a Class 4.6 or equivalent mild steel — not a substitute for a marked Class 6 or Class 8 in a structural application. Finishes: plain (self-colour, mild carbon steel), zinc-plated (BZP), hot-dip galvanised (HDG), and stainless steel. For guidance on when stainless or galvanised finishes are needed, see our Stainless Steel Fastener Grades guide. Thin Nut (Jam Nut / Half Nut) A thin nut is approximately half the height of a standard hex nut. It is called a "jam nut" or "half nut" when used in a two-nut locking assembly; the trade and catalogue term in Australia is typically "thin nut." The two legitimate uses of thin nuts are: first, as part of a jam-nut pair — two nuts on the same thread, tightened against each other. The method is to fit a thin nut first, partially tighten it, then fit a full nut on top and tighten the full nut hard against the thin nut. The reaction load between the two creates a locking effect. Correctly executed, this is a reliable locking method used in adjustable mechanical assemblies (valve adjusters, turnbuckles, jig fixtures). Second, in applications where the available thread protrusion is insufficient for a full-height nut, a thin nut may fit where a standard nut will not. The critical misuse to avoid: substituting a thin nut for a full nut in a single-nut application because a full nut is unavailable or does not fit. A thin nut used alone has significantly lower proof load than a full nut of the same class — the reduced thread engagement means the nut threads will strip at a lower force than the bolt will yield. This is a joint failure mechanism, not a design choice. Nyloc Nut (Nylon Insert Lock Nut) The nyloc nut is the most commonly specified lock nut in Australian trade and industrial work. It has a standard hex body with a full-height thread section below, and a nylon insert ring pressed into the top of the nut body. The nylon insert has no pre-formed thread — when the nut is driven down a bolt, the bolt thread cuts into the nylon and the compressed nylon grips the thread flanks under spring pressure. This interference creates friction that resists the nut backing off under vibration or dynamic load. The nyloc nut provides locking through friction only, not through mechanical interlock. The friction is reliable and effective within its rated operating conditions, but it can be overcome by sufficient axial load or loss of the nylon's elastic properties. Two conditions degrade nyloc performance significantly: Temperature: Nylon retains its elastic properties between −40°C and approximately +120°C. Above 120°C, the nylon softens and loses its grip on the thread flanks — the nut is no longer effectively locked. Below −40°C, nylon becomes brittle and may crack during installation. Nyloc nuts must not be used near heat sources: exhaust manifolds, flue connections, kilns, ovens, furnace components, or any assembly that regularly reaches above 100°C in service. The correct alternative for high-temperature applications is a prevailing torque all-metal lock nut or a castle nut with split pin. Reusability: Each time a nyloc nut is removed and reinstalled, the nylon insert undergoes additional deformation. Locking effectiveness diminishes with each cycle. The general guideline is that a nyloc nut may be reused if: the nut turns freely by hand when run down the thread (before the nylon engages), the nylon insert is intact with no cracking or deformation, and the thread is undamaged. In critical applications — structural bolting, load-bearing connections, anything where progressive loosening could cause injury — replace the nyloc nut on every disassembly. Nyloc nuts are available in Class 04 (a thin-body variant, lower profile), Class 6, Class 8, and Class 10. The class rating refers to the proof load of the metal body — the nut must still be matched to the bolt grade for strength. A Class 6 nyloc nut on a 10.9 bolt gives you nyloc locking action but insufficient thread engagement strength — the nut body will strip before the bolt yields under full load. Match property class to bolt grade. DIN 985 specifies the thin-body (half-height) nyloc; DIN 982 specifies the regular-height nyloc. Regular-height nylocs are the standard stock item in AU. For stainless nyloc nuts, the nylon insert is standard nylon — the limiting temperature remains +120°C regardless of the stainless body material. Shop nylon lock nuts: AIMS Nylon Lock Nuts For the full reference — DIN 985 vs DIN 982, the 120°C temperature ceiling explained, reuse decision rules, all-metal Stover and threadlocker alternatives, and matching nyloc grade to bolt grade — see our dedicated Nyloc Nut Guide. Prevailing Torque Nut (All-Metal Lock Nut) A prevailing torque nut achieves vibration resistance without nylon. Locking is built into the metal geometry of the nut itself — either through a distorted or elliptical top section, a tri-lobular thread form in the upper portion, or a section of thread that is slightly out-of-round relative to the bolt thread. When the nut is driven past the undistorted section and reaches the prevailing torque zone, the interference between the nut's deformed metal and the bolt thread creates resistive torque that must be overcome for the nut to turn in either direction. The key advantage over nyloc is temperature resistance. All-metal prevailing torque nuts can operate at temperatures far beyond the nylon limit — typically 200°C or higher depending on material, making them the correct choice for exhaust systems, near-engine applications, kiln equipment, and any assembly where service temperature exceeds the nyloc limit. The trade-off is higher installation torque — more force is required to drive a prevailing torque nut down the thread compared to a standard nut, because the interference is present throughout the thread engagement rather than only at the insert zone. This makes them less convenient for high-volume assembly. They are also generally more expensive than nyloc nuts of the same size. Common types: Philidas nut (distorted thread), Stover nut (conical top section), and elliptical-profile lock nuts. All are classed under the prevailing torque nut category in AS/NZS and ISO standards. Flange Nut A flange nut has a standard hex body with an integrated circular flange on the bearing face. The flange acts as a captive washer: it distributes the bearing face load across a larger contact area than the nut face alone, reducing surface stress on the clamped material. Because the washer is integral, there is no risk of forgetting or losing a separate washer during assembly. The non-serrated (smooth) flange nut does not bite into the mating surface. This makes it appropriate for applications where surface damage is unacceptable: painted surfaces, anodised aluminium, coated panels, and soft substrates. It is not a locking nut in the vibration-resistance sense — the smooth flange increases bearing area but does not significantly increase rotational resistance beyond that of a standard hex nut with a washer. Flange nuts are common in automotive applications (particularly in suspension and exhaust systems, where the broader bearing face compensates for oversized clearance holes), in machinery assembly where a separate washer step is to be eliminated, and in pipe and structural flange connections. Serrated Flange Nut The serrated flange nut adds radial or angular serrations to the bearing face of the flange. When tightened, these serrations bite into the mating surface, creating a mechanical interlock that resists rotation. The serrations work like a one-way ratchet against the surface — under vibration, the tendency to loosen is resisted by the serrations re-engaging the surface marks they have already created. This makes the serrated flange nut a legitimate locking nut, not just a load-distributing nut. It is widely used in automotive chassis assembly, engine bay components, and machinery where vibration is present and a separate locking method (nyloc, thread locker) is inconvenient or inappropriate. The limitation is the surface contact requirement. Serrated flange nuts should not be used on: plated or coated surfaces where the coating provides corrosion protection (the serrations cut through the coating); anodised aluminium (serrations destroy the anodise layer); painted cosmetic surfaces (visible scoring); soft materials like plastic or composite panels (serrations can crack or over-stress the substrate). For these surfaces, a smooth flange nut with a separate spring or star washer provides locking without destructive serration. Wing Nut The wing nut has two large flat wings projecting radially from the nut body, providing enough lever arm for the nut to be tightened and loosened by hand without any tools. It is the correct choice where frequent manual adjustment or quick release is needed and where vibration or high torque loads are not present. Common Australian applications: battery terminal nuts (positive and negative clamps), dust extraction hose couplings, machine cover panels requiring routine access, air filter canisters, temporary assembly work, and test fixtures. The wing nut is the right answer to the question "how do I fasten this so I can undo it by hand in thirty seconds?" For the full reference covering DIN 315 vs DIN 315 A, stamped vs cold-formed vs forged, sizing M3 to M24, and material selection, see our Wing Nut Guide. Wing nuts are not appropriate for structural load, vibration environments, or any application where the nut may be contacted by a rotating component or moving part. The projecting wings are a snagging and entanglement hazard in rotating machinery — the same prohibition that applies to gloves at rotating equipment applies here. Wing nuts in machinery enclosures should only be used on panels that are always stationary when the machine is running. Shop wing nuts: AIMS Wing Nuts Castle Nut (Castellated Nut) A castle nut has a standard hex body below, topped by a cylindrical crown section with slots machined through it at regular intervals around the circumference. In use, a split pin (the Australian term for what Americans call a cotter pin) is passed through two opposing slots in the crown and through a cross-hole drilled through the bolt or stud. The split pin's legs are bent outward on the other side to prevent withdrawal. The result is a positive mechanical lock: the nut physically cannot rotate because the split pin bridges the nut slots and the bolt hole. This positive lock does not rely on friction, nylon properties, metal deformation, or any mechanism that degrades over time and temperature. The castle nut with split pin will hold as long as the split pin is intact and the bolt cross-hole is undamaged. This is why it is the specified fastening method in safety-critical, low-torque, or high-consequence applications where gradual loosening would be catastrophic. The primary AU applications are trailer wheel hub bearings, boat trailer wheel bearings, and light vehicle front wheel hub assemblies where a tapered roller bearing is retained by a castle nut running on the stub axle. The installation procedure is specific: tighten to specified torque to seat the bearing, then back off to the nearest slot that aligns with the cross-hole, insert the split pin, and bend. The nut is deliberately not torqued to maximum — the bearing requires controlled end-float, and over-tightening destroys the bearing rapidly. Other applications: tow hitch pin retention, steering linkage rod ends, suspension pivot pins, and any pin joint where vibration loosening would cause component separation. Castle nut vs slotted nut: These are sometimes used interchangeably, but there is a difference. A castle nut has a distinct cylindrical crown section above the hex — the slots are only in the crown, and the hex below is full height. A slotted nut has slots machined through the full hex height, with no separate crown section. The castle nut's crown geometry confines the split pin closer to the nut axis, which some engineers prefer for positive retention. In practice, both work correctly with a split pin through matching bolt cross-holes. Dome Nut (Acorn Nut / Cap Nut) A dome nut — also called an acorn nut or cap nut — has a standard hex body below and a closed domed cap at the top. The dome encloses the bolt thread end, protecting it from corrosion, impact damage, or contamination. The smooth domed exterior also provides a clean, finished appearance and eliminates the exposed sharp thread end that can cause cuts and snagging. Dome nuts are used where: the thread end will be exposed to the weather or corrosive atmosphere; the assembly is in a location where contact with a sharp thread end is a safety concern (handrail fittings, public furniture, playground equipment, marine fixtures); or a finished appearance is required (consumer products, display fittings, architectural metalwork). The thread depth inside the dome is limited — the nut can only accept a bolt that protrudes a specific number of threads into the dome cavity. Bolts that protrude too far cannot be fully tightened (the bolt end bottoms out in the dome before the nut clamps the joint). Always check thread engagement against the dome nut's internal cavity depth when selecting size. Available in stainless steel, zinc-plated steel, and brass. Stainless dome nuts are a common choice for outdoor handrail and balustrade assemblies in coastal environments where both corrosion resistance and appearance matter. Shop dome nuts: AIMS Dome Nuts Coupling Nut (Extension Nut) A coupling nut is a long hex nut — typically three times the length of a standard hex nut at the same diameter — used to join two lengths of threaded rod end-to-end, or to thread onto a stud and extend it. The long body provides thread engagement with both male thread ends simultaneously, and the hex exterior accepts a spanner for tightening. The most common application in Australian construction and industrial work is suspended ceiling systems: threaded rod is hung from the structural slab, coupling nuts are used to extend the rod downward to the ceiling grid level when a single rod length is insufficient. Coupling nuts are also used in pipe support hangers, conveyor structure, industrial platforms, and any application involving long threaded rod assemblies. Coupling nuts are available in metric and imperial thread forms. Metric DIN 6334 is the standard specification. Full-thread coupling nuts accept the same thread throughout their length — both rods must be the same diameter and pitch. Reducing coupling nuts accept different sizes at each end — useful for thread size transitions. T-Nut (Tee Nut) A T-nut (tee nut) consists of a threaded barrel (the nut body) with a flat circular or square flange at one end and two or more sharp prongs projecting from the flange in the same axial direction as the barrel. Installation requires a pre-drilled hole in a timber or sheet material substrate. The barrel is inserted into the hole from one face; the prongs are driven into the surrounding timber surface (or the flange is seated against the substrate face) to anchor the nut rotationally; a bolt from the opposite face drives into the barrel and draws a cap or cover tight, pulling the flange flush against the hole face. T-nuts provide a reusable threaded insert in wood, MDF, and similar substrates — materials that cannot themselves hold adequate thread engagement for repeated assembly and disassembly. They are standard in: furniture joinery (bed frames, shelf units, table aprons), woodworking jig boards and fixture tables, architectural joinery, and flat-pack cabinet construction where a durable threaded point is required at a specific location. T-nuts are not used in metal-to-metal assemblies — they are a wood/sheet fastener. For a captive threaded insert in metal sheet, the weld nut or a threaded insert insert (helicoil, rivet nut) is the correct choice. Barrel Nut (Furniture Connector Nut) A barrel nut is a cylindrical (not hexagonal) nut with a threaded cross-hole through its diameter rather than through its length. Installation requires two holes: one through-hole for the connecting bolt (perpendicular to the joint face) and one cylindrical recess hole (parallel to the joint face) into which the barrel body sits. The bolt passes through the panel or timber, enters the barrel's cross-hole, and is tightened — drawing the joint together. The barrel nut is completely enclosed in its recess and invisible in the assembled joint. Barrel nuts are the standard concealed fastener in flat-pack and ready-to-assemble (RTA) furniture: beds, bookshelves, flat-pack wardrobes, and office furniture. They are also used in timber frame construction where a clean face is required, in exhibition stand joinery, and in modular equipment structures. The concealed installation means no protruding fastener heads on any face of the joint. Most commonly encountered in M6 and M8 metric thread sizes. Usually supplied in bright zinc or nickel-plated steel for furniture applications. The bolt that engages the barrel nut typically has a pan or button head — recessed in the through-hole face. Weld Nut A weld nut is a nut specifically designed for welding to a parent material — typically a steel panel or structural member — to create a captive threaded point. Once welded, a bolt can be fastened from the accessible side only, without any nut access from behind. This is essential on thin panels, hollow sections, and assembled structures where the nut side is enclosed. The most common types are the square projection weld nut (DIN 928) and the hex flange weld nut. Projection weld nuts have small raised projections on the bearing face that concentrate the welding current and create localised weld points. Flange weld nuts have a broad flange that seats flush against the panel surface and are typically MIG or spot-welded around the flange perimeter. Weld nuts are standard in automotive body manufacture, equipment frames, electrical enclosures, and any sheet metal assembly where the blind-side access problem exists. The parent material must be weldable steel — weld nuts cannot be used on aluminium panels with standard welding, stainless without appropriate welding procedure, or galvanised sheet (the zinc coating releases toxic fumes and prevents a clean weld). Nut Property Classes — Class 5, 6, 8, 10, 12 Explained The property class stamped on a metric nut is a mechanical performance designation, not a material specification. It tells you the proof load the nut can sustain without stripping, which determines what bolt grade the nut can be paired with to develop the bolt's full rated load. The relevant Australian standard is AS 1112 (hex nuts) and AS/NZS 4291.2 (mechanical properties), which aligns with ISO 898-2. The property class system for nuts differs from the bolt grade marking system — bolt grades are two numbers separated by a decimal point (4.6, 8.8, 10.9); nut classes are single numbers (5, 6, 8, 10, 12) or two-digit codes (04 for thin nuts). Do not confuse the nut class number with the bolt grade number even where they appear similar. Class 5 General commercial grade. Used with Class 4.6 and 5.6 bolts. Not marked with a class number on most commercially available nuts — unmarked hex nuts in general trade supply are typically equivalent to Class 5 or lower. Not appropriate for structural applications or high-tensile bolt assemblies. Class 6 The standard general-purpose nut class in Australian supply. Matched to 8.8 bolts in general mechanical and construction applications. This is the most commonly stocked nut class in AU. A Class 6 hex nut is marked "6" on the face or flats. When a drawing specifies "hex nut, class 6" this is what is ordered. Class 8 High-tensile nut. Required when paired with 8.8 bolts in structural applications, and when paired with 10.9 bolts in general applications. Marked "8." Available in standard hex and in nyloc variants (Class 8 nyloc). The nut must be able to develop the bolt's full proof load — pairing an 8.8 bolt with a Class 6 nut in a structural joint risks thread stripping at the nut before the bolt yields. Class 10 Matched to 10.9 bolts. Marked "10." Used in high-strength structural connections, machinery, and critical fastened joints. Less common in general supply — typically a special-order or heavy-industrial item. Class 12 For 12.9 bolts. The highest standard property class for commercial metric nuts. Marked "12." Specialist application — precision machinery, tooling, critical fastened joints. Not a standard stock item at most AU suppliers. Class 04 The thin (half-height) nyloc nut class. The "0" prefix denotes thin height. Used in applications where the standard nyloc height does not fit. Lower proof load than full-height nyloc — verify thread engagement is adequate for the application. For full bolt grade markings and the matching of bolt grades to application requirements, see our Bolt Grade Chart guide. Matching Nut Class to Bolt Grade The fundamental rule: the nut must be capable of sustaining at least the full proof load of the bolt it is paired with, without stripping. Using an under-classed nut does not reduce the bolt's rated tension capacity — the bolt will attempt to develop its full proof load during tightening, and the under-classed nut threads will strip first. The joint fails in a way that is not visible from outside the assembly. Bolt Grade (metric) Minimum Nut Class Typical application 4.6 Class 5 General structural steel, light fabrication 5.6 Class 5 General structural 6.8 Class 6 General mechanical, machinery 8.8 Class 8 High-tensile structural, heavy machinery 10.9 Class 10 Critical structural, high-load connections 12.9 Class 12 Precision machinery, critical high-strength joints Note for imperial fasteners: the SAE Grade system (Grade 2, 5, 8) does not correspond directly to the ISO property class system. Grade 2 nuts pair with Grade 2 and Grade 5 bolts; Grade 5 nuts pair with Grade 5 bolts; Grade 8 nuts pair with Grade 8 bolts. Do not cross-reference SAE grades and ISO property classes as if they are equivalent. For more on identifying bolt grades and markings, see our Bolt Grade Chart. Which Locking Nut Should You Use? The choice between locking nut types comes down to four factors: operating temperature, whether surface marking is acceptable, whether the nut will be removed and reinstalled, and whether a positive mechanical lock (castle nut) is required by the application or relevant standard. Locking method Max temp Surface marking Reusable? Positive lock? Best for Nyloc nut +120°C None Limited No General vibration resistance, most industrial applications below 120°C Serrated flange nut +300°C+ Yes — bites surface Yes (new surface marks) No Automotive, chassis, exhaust, unpainted structural steel Prevailing torque (all-metal) +200°C+ None Yes (limited cycles) No High-temperature applications, exhaust, near-engine components Castle nut + split pin Unlimited None Yes (replace split pin) Yes Wheel hub bearings, safety-critical joints, regulatory requirement Thin nut + full nut (jam pair) Unlimited None Yes No (friction) Adjustable assemblies, turnbuckles, jig fixtures Shop lock nuts: AIMS Lock Nuts | Hex Lock Nuts Quick Selection Guide Application Recommended nut Key reason General bolted assembly, structural steel Hex nut (Class 6 or 8) Standard, correct class for bolt grade Vibration environment, below 120°C Nyloc nut Reliable friction locking, widely available Vibration, above 120°C or near heat source Prevailing torque nut All-metal locking, no nylon temperature limit Automotive chassis, unpainted structural steel Serrated flange nut Bites surface, vibration resistance, no separate washer Wheel hub bearings, trailer axles Castle nut + split pin Positive mechanical lock, standard AU trailer requirement Quick hand-release (battery terminals, covers) Wing nut No tools required, fast on/off Exposed thread end protection (outdoor, cosmetic) Dome nut Encloses thread, corrosion and injury protection Joining two lengths of threaded rod Coupling nut Full thread engagement both rods, hex drive Timber/MDF threaded insert (furniture, jigs) T-nut Provides reusable thread in non-metallic substrate Concealed joint in furniture or timber frame Barrel nut Invisible when assembled, clean face on all panels Thin panel, bolt access one side only Weld nut Captive thread, no back-access required Locking two nuts against each other Thin nut + full nut pair Jam nut locking, adjustable assemblies Coated or soft surface, load distribution needed Smooth flange nut Wide bearing face, no surface damage Frequently Asked Questions What is the difference between a nyloc nut and a standard hex nut? A standard hex nut relies on friction between the bolt thread flanks and nut thread flanks to resist loosening. Under vibration or dynamic load, this friction can be overcome progressively — the nut backs off. A nyloc nut adds a nylon insert ring at the top of the nut body. When the nut is tightened, the bolt thread deforms the nylon, and the nylon grips the thread under spring pressure. This additional friction significantly increases resistance to vibration loosening. The trade-off is a temperature limit of approximately +120°C (above which the nylon softens and loses its grip), reduced effectiveness after multiple removal and reinstallation cycles, and slightly higher installation torque. Can I reuse a nyloc nut? Yes, with limitations. Each time a nyloc nut is removed and reinstalled, the nylon insert undergoes additional deformation and its locking effectiveness diminishes. For non-critical applications, a nyloc nut that shows no cracking, runs freely on the thread before the nylon engages, and has an intact insert can be reused. For critical applications — structural connections, load-bearing assemblies, safety-related joints — replace the nyloc nut on every disassembly. A nyloc nut costs a fraction of the labour involved in disassembly; replacing it is the correct practice in critical applications. What is a castle nut and when should I use one? A castle nut has a cylindrical crown with slots above its standard hex body. A split pin passes through the slots and a cross-hole in the bolt or axle, physically preventing the nut from rotating. Use a castle nut wherever a positive mechanical lock is required: trailer wheel hub bearings, boat trailer axles, steering linkage pins, and tow hitch retaining nuts. The positive lock does not rely on friction or nylon — it is as secure as the split pin is intact. The paired bolt or stud must have a pre-drilled cross-hole for the split pin to pass through. Nyloc vs serrated flange nut — which is better for vibration? Both are effective, but for different conditions. Nyloc nuts rely on nylon friction — effective below 120°C, no surface damage, limited reusability. Serrated flange nuts rely on serrations biting into the mating surface — effective at high temperatures, no nylon limit, but the serrations mark the surface and are unsuitable for coated, painted, or soft substrates. For general indoor machinery below 120°C, a nyloc is simpler and neater. For automotive chassis, unpainted structural steel, or applications above the nyloc temperature limit, the serrated flange nut is the better choice. What property class nut should I use with an 8.8 bolt? Class 8. An 8.8 bolt in a structural application requires a Class 8 nut to develop the bolt's full proof load without the nut stripping. In non-structural or general-purpose applications, a Class 6 nut is sometimes used with 8.8 bolts, but this is only appropriate where the assembly torque is well below the nut's stripping point. For any bolted joint where the bolt is torqued to specification, the nut must match or exceed the required class. The nut marking is stamped on the bearing face or flats — "8" denotes Class 8. What is the difference between property class and grade for nuts? Property class is the ISO/metric designation for nut strength (Class 5, 6, 8, 10, 12) used in Australia under AS 1112. Grade is the SAE/imperial designation (Grade 2, 5, 8) used on American-specification fasteners. They are different systems and cannot be directly cross-referenced numerically. A metric Class 8 nut and an imperial Grade 8 nut are not equivalent — they have different mechanical properties, thread forms, and dimensional standards. When mixing metric and imperial in older plant or equipment, identify the actual thread form before selecting replacement nuts. Can nyloc nuts be used at high temperatures? No — not above approximately +120°C. The nylon insert softens above this temperature and loses its grip on the bolt thread. The nut becomes a standard hex nut without effective locking. For applications above 120°C — near exhaust systems, in ovens, kilns, near welding, or on industrial process equipment — use a prevailing torque all-metal lock nut, a serrated flange nut, or a castle nut with split pin. The operating temperature of the assembly determines which locking method is appropriate, not just the ambient air temperature. What is a prevailing torque nut? A prevailing torque nut achieves vibration resistance through the metal geometry of the nut itself — a distorted thread, elliptical profile, or tri-lobular form in the upper thread section creates interference with the bolt thread throughout installation and removal. No nylon is involved, so there is no temperature limit from the insert. The nut provides resistive torque against both tightening and loosening — the torque required to drive it exceeds that of a standard nut. This makes it the correct replacement for a nyloc nut in any application where service temperatures exceed the nyloc limit. What is a coupling nut used for? A coupling nut is used to join two male-threaded components end-to-end — most commonly two lengths of threaded rod, or a stud and a threaded rod. It is a long hex nut (approximately three times the standard length) that threads onto both components simultaneously, with its hex exterior accepting a spanner for tightening. The most common application in Australian construction is suspended ceiling systems, where coupling nuts extend threaded rod hangers to the required ceiling height. They are also used in pipe support systems, conveyor structures, and industrial frame assemblies involving long threaded rod runs. What is the difference between a dome nut and a cap nut? Nothing — they are the same fastener, referred to by different names. The standard catalogue term in Australian supply is "dome nut." The term "cap nut" or "acorn nut" (from the shape resemblance) is also used, particularly in older catalogues and American technical literature. All refer to the hexagonal nut with a closed domed top that covers and protects the exposed bolt thread end. When ordering, dome nut and cap nut will return the same product category. What does "full nut" mean? In Australian trade, "full nut" means a standard-height hex nut — specifically, a hex nut of the normal (non-thin) height as specified in AS 1112.1. The term distinguishes the standard nut from a thin nut (half nut, jam nut), which is approximately half the height. A "full nut" provides full thread engagement to develop the bolt's proof load. When a trade counter asks if you need a "full nut or a thin nut," this is the distinction being made. Which nuts can be used in outdoor or corrosive environments? Stainless steel (304 or 316) is the correct material for nuts exposed to weather, moisture, salt spray, or corrosive process environments. 316 stainless is specified for coastal and marine environments and anywhere chloride exposure is expected. Hot-dip galvanised (HDG) hex nuts are appropriate for structural outdoor applications — HDG provides thick zinc coating that gives extended protection in most atmospheric environments but is not appropriate for immersion or chemical exposure. Zinc-plated (BZP) nuts provide minimal corrosion protection and are not suitable for exposed outdoor use. For full guidance on finishes, see our Stainless Steel Fastener Grades guide. Shop Nuts at AIMS Industrial AIMS Industrial stocks the full range of metric and imperial nut types across all common property classes and finishes — hex nuts, nyloc nuts, flange nuts, dome nuts, castle nuts, wing nuts, coupling nuts, weld nuts, and more. Available in zinc-plated, hot-dip galvanised, and stainless steel (304 and 316). Shop All Lock Nuts Nylon Lock Nuts Pair this guide with our Tap Drill Size Chart for the right pilot drill diameter at every tap size. For thread specs, grade markings and metric-to-imperial conversions, see our Fastener Reference Guide. For powder, granular, and bulk-material flow aid, see the AIMS industrial pneumatic vibrator range. For lang tools, see our lang tools range stocked across Australia.
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Read moreIndustrial Shim Guide: Types, Materials & How to Choose
What is a shim? A shim is a thin precision-cut spacer used to align, level, or take up clearance between two mating parts. Common applications include aligning pump-to-motor couplings, levelling machinery baseplates, setting bearing preload, taking up wear in journal bearings, and adjusting press-tool die height. Industrial shims come as flat sheets, pre-cut slotted shapes (for in-situ installation under bolted feet), or laminated peelable stacks where individual layers can be removed to fine-tune thickness. A shim is one of the most underrated items in a maintenance fitter's toolkit. Half a millimetre of steel — cut from a roll and slipped under a motor foot — is the difference between a pump that runs reliably for five years and one that consumes bearings every six months. In construction, a plastic packer wedged under a door frame costs almost nothing and saves a door that would never hang correctly. In a precision engine, a valve shim ground to 0.025 mm changes everything about how that engine performs. Despite their simplicity, shims are widely misunderstood. People confuse them with washers and spacers. They stack too many. They reach for a cedar wedge when the job needs precision steel. They choose the wrong material for the environment — and end up with corroded steel in a food plant or deformed plastic under a two-tonne motor. This guide covers the full picture: what shims are, how they differ from washers and spacers, every type you will encounter in Australian industry and construction, how to select the right material, how to choose and measure thickness, the rules around stacking, structural and load-bearing considerations, and specific applications from machinery alignment to excavator pins. Written for the Australian trade and industrial market, with products stocked at AIMS Industrial from Champion and Precision Brand. Shim Materials: Steel, Brass, Stainless & Plastic Compared — Quick Reference Material selection is where shim choices most often go wrong. The wrong material in the wrong environment corrodes, deforms, or introduces contamination. Material Strength Corrosion Resistance Relative Cost Best Applications Cold-rolled steel High Low — will rust Low General industrial, dry indoor environments, machinery alignment Stainless steel 304 High Excellent Medium Food processing, pharmaceutical, washdown environments Stainless steel 316 High Excellent (chloride) Medium–high Marine, coastal, chemical plant, chlorinated water Brass Medium Good (atmospheric) Medium Electrical equipment, precision instruments, non-magnetic applications Aluminium Low–medium Good Medium Aerospace, lightweight applications HDPE / PP plastic Low Excellent Very low Construction framing, door and window installation What Are Shims and What Do They Do? A shim is a thin, flat piece of material inserted between two surfaces to fill a gap, correct alignment, level a component, or achieve a precise fit. The principle is ancient — craftspeople have been using wedges and spacers to compensate for imperfect dimensions since before recorded engineering. The materials and tolerances are modern; the idea is not. The core function of a shim is to compensate for dimensional variation that cannot be designed or manufactured out of a system. No surface is perfectly flat. No concrete slab is perfectly level. No motor foot sits at exactly the right height after installation on a real-world base. Shims correct for the imperfection that engineering drawings assume away — they are the bridge between the ideal dimension and the actual one. In practice, shims perform four distinct functions: Gap filling — closing a space between two mating surfaces with precise control over the final gap dimension (e.g., head gasket shims, cylinder head shims, bearing cap shims) Alignment correction — raising or lowering one side of a machine to achieve shaft concentricity and angularity within specification (e.g., motor foot shimming, pump alignment, gearbox installation) Levelling — bringing a surface to a known datum, typically horizontal, so a machine or structure sits correctly (e.g., levelling a machine tool on a slab, a base plate for a column, a structural beam bearing) Preload and clearance adjustment — setting the force applied to a spring, bearing, or valve element (e.g., valve train shims for tappet clearance, differential bearing preload, hydraulic relief valve pressure setting) The applications span every industrial sector in Australia: manufacturing, food processing, mining, civil construction, marine, agricultural equipment, and automotive. Anywhere two components need to fit precisely — and the precision cannot be machined in after the fact — a shim is the answer. Shims are cheap. The consequence of getting them wrong is not. A misaligned motor on the wrong shim stack runs hot, vibrates, and fails prematurely. A door frame packed with a timber offcut shifts over time and the door sticks. A base plate shimmed with compressed plastic settles and the column goes out of plumb. Use the right shim for the job. Shims vs Washers vs Spacers: Key Differences Explained The confusion between these three items comes from appearance — they all look like flat things that go between surfaces. The function is where they diverge, and understanding the difference matters for selecting the right component. What a Washer Does A washer is a fastener component. Its job is to distribute the clamping load from a bolt head or nut across a larger surface area, preventing the fastener from embedding into soft material or pulling through a large hole. Spring washers (Belleville or helical) add a locking function. Repair washers have an oversized outer diameter for use with damaged holes. Washers are manufactured to loose dimensional tolerances — a standard flat washer to DIN 125 or AS 1237 has a nominal thickness but that thickness is not a precision measurement. You would never use a standard washer to fill a 0.15 mm gap — you have no reliable idea what thickness you are actually installing. Washers go under fasteners. They do not fill precision gaps. What a Spacer Does A spacer maintains a fixed, known distance between two components. Spacers are typically thicker than shims — often a machined cylindrical or tubular component — and their purpose is to hold components at a set distance during assembly. Wheel spacers on a vehicle hub, standoffs in an electronics enclosure, and bearing spacers in a gearbox are all spacers. They are not adjustable. They set a dimension and hold it. What a Shim Does A shim is the adjustment tool. It is manufactured to tight thickness tolerances specifically so that you can select — or cut to — the exact dimension you need to fill a measured gap or correct a measured misalignment. The tolerance of quality shim stock is plus or minus 0.003 mm or better. That is the whole point: you measure, you select, you trust the result. In summary: washer = distributes clamping load under a fastener. Spacer = holds components at a fixed set distance. Shim = fills a measured gap, corrects alignment, achieves a precise fit. There is one area where the terms overlap: in structural and heavy equipment work, a thick steel plate used under a base plate may be called a shim plate in some documentation even though it functions more like a spacer. What matters is the function — precision gap filling and adjustment — and selecting material manufactured to tight enough tolerances to do it reliably. Types of Shims: A Complete Overview The shim category is broader than most people realise. Understanding the different types — and what each is designed for — prevents the wrong type ending up in the wrong application. Shim Stock (Rolls and Flat Sheets) Shim stock is precision-rolled metal available in continuous rolls or flat sheets at controlled thicknesses. The user cuts the shim to any shape required — custom footprints, specific slot positions, unusual profiles. This is the most versatile shim format, and it is what most people mean when they refer to "shim stock." Standard widths for rolls are 150 mm or 300 mm. Sheet sizes vary by supplier — 300 × 300 mm and 300 × 600 mm are common. Thicknesses range from 0.025 mm (1 thou) to 3.0 mm or heavier, with a full range of intermediate gauges. AIMS stocks shim stock in cold-rolled steel, stainless steel 304 and 316, and brass from Precision Brand and Champion. Slotted Shims (Horseshoe Shims / Alignment Shims) Slotted shims — called horseshoe shims or U-shims in the trade — have a slot cut from one edge through to a central opening. The slot allows the shim to slide around a bolt or shaft without removing the fastener. You loosen the hold-down bolt, slide the shim stack in or out, then re-torque. This design is the standard for motor and machinery alignment work. The machine does not need to be completely disassembled to adjust the shim stack — a significant time saving on any alignment job. Slotted alignment shim kits include multiple thicknesses so the technician can build the required correction by stacking. AIMS stocks these kits for standard motor foot sizes. Tapered Shims A tapered shim has a wedge profile — thicker at one end, thinner at the other — giving a uniform taper across its length. Tapered shims are used to correct angular misalignment, where one side of a component sits higher than the other and a uniform-thickness shim would not resolve the angular error. They appear in structural steel work (under base plates on slightly sloped concrete), in some machinery installations, and in automotive applications. Two tapered shims pushed in from opposite ends create an effective shim of adjustable thickness — a useful field technique when standard thicknesses are not available. Laminated (Peelable) Shims Laminated shims consist of multiple thin metal layers bonded together into a single assembly. When the total assembled thickness is too much, individual layers are peeled off to reduce thickness — no cutting required. The precision of each remaining layer is maintained because the layers are controlled during manufacture. Laminated shims are used in production tooling, precision fixtures, and applications where fast, clean adjustment matters without the complexity of managing a loose multi-piece stack. They cost more than plain shim stock but eliminate several practical problems. Plastic Shim Packers (Construction Packers) Plastic packers — called shim packers in the Australian construction trade, or simply "packers" on site — are non-compressible plastic blocks used to level and align frames, windows, doors, and structural elements. Made from HDPE or polypropylene, they are moisture-resistant, do not rot, do not compress under construction loads, and are UV-stable. Plastic packers are stackable and come in standard widths (28 mm, 68 mm, 100 mm) and thicknesses from 1 mm to 20 mm. They are a construction-site daily consumable in Australia — every joinery and framing installation uses them. Valve Shims Valve shims are precision-ground discs used in overhead cam engines to set valve clearance (tappet clearance). They sit between the cam follower (bucket) and the valve stem end. The clearance is measured with a feeler gauge and the shim thickness is selected from a range — typically in increments of 0.025 mm or 0.05 mm — to bring the clearance within the manufacturer's specification. Brake Shims Brake shims are anti-squeal pads bonded to the back of disc brake pads, or inserted between the pad and the caliper piston. They dampen vibration and reduce brake noise. This is a specific automotive application outside AIMS's core industrial range but worth noting as a distinct shim category — a brake shim is not interchangeable with a machinery alignment shim. Cylinder Head and Gasket Shims In high-performance engine building, cylinder head shims adjust compression ratio or correct deck height after machining. They sit between the cylinder head and engine block, on top of the head gasket. These are precision components manufactured to very tight flatness and thickness specifications. Shim Materials: Steel, Brass, Stainless & Plastic Compared Material selection is where shim choices most often go wrong. The wrong material in the wrong environment corrodes, deforms, or introduces contamination. Here is a clear comparison of each material's properties and the applications they suit. Cold-Rolled Steel (CRS) Cold-rolled steel shim stock is the most widely used industrial shim material. It offers high compressive strength, consistent thickness tolerances, excellent formability, and low cost. The manufacturing process — rolling at room temperature — produces a smooth, bright surface finish and tight dimensional control. The limitation is corrosion: uncoated cold-rolled steel will rust in any environment with moisture, chemicals, or salt. In dry indoor environments, steel shims are the default choice. In outdoor, wet, chemical, or food-processing environments, upgrade to stainless steel. Stainless Steel 304 Grade 304 stainless steel (18% chromium, 8% nickel) handles water, most dilute acids and alkalis, organic compounds, and general industrial chemical exposure without significant corrosion. It is the standard material for food processing equipment, pharmaceutical plant, and any application requiring regular washdown with detergents or sanitisers. Stainless 304 shim stock costs roughly two to three times more than equivalent carbon steel, but in corrosive environments that cost premium pays back in reliability. Stainless Steel 316 Grade 316 adds 2–3% molybdenum to the 304 composition, providing superior resistance to chloride-induced pitting corrosion. 316 is the correct choice for marine environments, coastal installations, chlorinated water systems, and chemical plants handling chlorine compounds or strong acids. If the application involves salt water, seawater spray, or aggressive chloride exposure, use 316 — not 304. Brass Brass shim stock is non-magnetic, has good thermal and electrical conductivity, and is soft enough not to score or gall precision mating surfaces. These properties make brass the preferred choice in electrical switchgear, precision instruments, and any application where magnetism would cause problems. Brass is softer than steel — do not use brass shims in high-load structural applications where the shim must resist deformation under compressive stress. Aluminium Aluminium shim stock is lightweight, corrosion-resistant in most environments, and easy to cut and form. It is used in aerospace, automotive, and applications where weight matters. Its lower compressive strength makes it unsuitable for heavy-load industrial shimming — use steel for machinery. Plastic (HDPE and Polypropylene) HDPE packers are the construction trade standard for framing and window installation: non-compressible under typical construction loads, moisture-proof, rot-proof, and UV-stable. Polypropylene packers are slightly stiffer and more brittle in cold conditions. Neither is appropriate under heavy industrial equipment — use steel for any machine base shimming application. Material Strength Corrosion Resistance Relative Cost Best Applications Cold-rolled steel High Low — will rust Low General industrial, dry indoor environments, machinery alignment Stainless steel 304 High Excellent Medium Food processing, pharmaceutical, washdown environments Stainless steel 316 High Excellent (chloride) Medium–high Marine, coastal, chemical plant, chlorinated water Brass Medium Good (atmospheric) Medium Electrical equipment, precision instruments, non-magnetic applications Aluminium Low–medium Good Medium Aerospace, lightweight applications HDPE / PP plastic Low Excellent Very low Construction framing, door and window installation Shim Stock: What It Is and When to Use It Shim stock is the raw form of the shim world — precision-rolled metal that you cut to the exact size, shape, and configuration you need. When no standard off-the-shelf shim fits the job, shim stock is the answer. Why Tolerance Matters The defining characteristic of quality shim stock is thickness tolerance. Precision Brand shim stock maintains thickness within plus or minus 0.003 mm for fine gauges (0.025 mm to 0.25 mm) and plus or minus 0.005 mm for heavier gauges. This means a shim labelled 0.127 mm (5 thou) is reliably 0.124–0.130 mm — narrow enough that you can trust the measurement when stacking shims to reach a calculated alignment correction. Low-grade shim material with wide thickness tolerances undermines the whole point of precision shimming. If your 0.1 mm shim is actually anywhere from 0.095–0.108 mm, your alignment calculation is invalid from the start. Standard Thickness Range Shim stock is available across a wide range of thicknesses. The Australian trade uses both metric and imperial (thou) designations — both systems are in active use. Common thicknesses: 0.025 mm (1 thou) — ultra-fine adjustment, precision instruments, valve shims 0.050 mm (2 thou) — fine machinery alignment, bearing preload 0.075 mm (3 thou) — general alignment work 0.100 mm (4 thou) — general alignment, one of the most used sizes 0.125 mm (5 thou) — very common for motor foot shimming 0.150 mm (6 thou) — standard alignment thickness 0.175 mm (7 thou) — intermediate correction 0.250 mm (10 thou) — heavier correction 0.500 mm, 0.750 mm, 1.000 mm — structural shimming and base work 1.5 mm, 2.0 mm, 3.0 mm+ — heavy structural shimming, excavator pins Conversion note: 1 thou (thousandth of an inch) = 0.0254 mm. If your alignment software outputs results in thousandths of an inch, convert before selecting shims. Many experienced alignment technicians in Australia work in thou by preference — both units are entirely valid. Roll vs Sheet Rolls are better for operations that regularly cut custom shims — continuous supply, easier to handle when cutting strips or long narrow pieces. Flat sheets are more practical for one-off jobs and benchtop cutting — the stock lies flat without the spring-back tendency of a roll. Both formats are available from AIMS across steel, stainless, and brass. When to Use Shim Stock vs Pre-Cut Shims Use shim stock when: the required shim shape is non-standard, the slot position does not match standard slotted shims, a continuous strip is needed, or you need a specific material and thickness not available pre-cut. Use pre-cut slotted shims when: doing standard motor alignment, speed matters, or you are working from a kit. Shimming for Machinery Alignment and Levelling Machinery alignment is the most consequential application for precision shims in Australian manufacturing, processing, and mining. Motor-to-pump alignment, gearbox installation, compressor mounting, conveyor drive shimming — all depend on shims at the machine feet to achieve shaft concentricity and angularity within the coupling manufacturer's specification. Why Alignment Matters A misaligned coupling generates vibration, uneven bearing load distribution, elevated operating temperature, and accelerated seal and coupling wear. Industry data consistently attributes 50% or more of premature rotating machinery failures to misalignment. The bearing that should last 40,000 hours fails in 8,000. The mechanical seal rated for two years goes in six months. The coupling insert that should last years needs quarterly replacement. Proper shimming and alignment is one of the highest-return maintenance activities in any plant. The cost of a set of alignment shims and an hour of a technician's time is a fraction of the cost of a failed bearing, an emergency motor rewind, or unplanned production downtime. Types of Misalignment Shims Correct Parallel (offset) misalignment — shaft centrelines are parallel but offset from each other. Corrected by moving the motor sideways (horizontal) or shimming feet (vertical). Angular misalignment — shaft centrelines meet at an angle. Corrected by shimming the front or rear feet of the motor by different amounts to change the shaft angle. Most alignment jobs involve both types simultaneously. Laser alignment equipment measures both and calculates the exact shim thickness required at each of the four feet. The Alignment Shimming Process Soft foot check first — Loosen each hold-down bolt in turn and measure whether the machine lifts. Soft foot creates measurement errors that make alignment impossible to achieve cleanly. Correct it by shimming the lifting foot until all four feet sit solidly. Measure misalignment — Laser alignment equipment or dial indicators measure offset and angularity. Laser systems calculate the required shim corrections at each foot automatically. Select shims — Choose slotted shims in the required thickness, or stack to achieve the total correction. Keep stacks to three or fewer shims where possible. Insert and torque — Slacken the hold-down bolt, slide the shim in, re-torque to specification, re-measure. Repeat until within coupling tolerance. Document the result — Record the final shim stack at each foot, pre- and post-alignment readings, and date. This is the baseline for the next alignment check. Levelling a Machine Base For new machine installations on a concrete slab, steel shims bring the base plate to level before the void is grouted. Place shim stacks at each support point, level with a precision spirit level or laser level to within 0.05 mm/m or better, then fill the void with non-shrink epoxy grout. The shims become a permanent load-carrying component embedded in the grout. Shim Packers in Construction: Doors, Windows and Frames In the Australian construction trade, "shim packers" or simply "packers" are a daily site consumable on any framing, joinery, or window installation job. The term is distinctly Australian — in the UK they are called packing pieces; in the US, shims or shim wedges. In Australia, ask for packers or shim packers. Why Frames Need Shimming No wall opening or floor surface is perfect. Concrete slabs have surface variation. Wall studs bow slightly. Masonry openings are rarely square. To install a door or window correctly — plumb, level, and square — the frame must be adjusted to compensate for the imperfection of the opening it sits in. Packers fill the gap between the perfect frame and the imperfect opening, allowing precise control of position without modifying either. Getting this right matters: a door frame that is not plumb creates a door that swings open or closed on its own, or binds in the frame. A window sill that is not level causes water pooling. Two minutes spent correctly packing a frame saves significant remediation later. Door Frame Installation Place packers at hinge locations (every hinge position must be backed by a packer so the fixing screw goes into solid material behind the frame), at the strike plate location, and at the head. Start at the bottom: set the first packer to bring the bottom of the hinge jamb to plumb and level, then work upward. Check plumb on both jambs and level on the head before fixing permanently. Window Frame Installation Window sills must be level across their full width — check with a long level and shim up the low end. Jambs must be plumb — shim at the top and bottom of each jamb as needed. Use the same stackable approach: measure the gap at each packer position and select the combination of thicknesses that fills it without gaps or forcing. Standard Packer Sizes Widths: 28 mm, 68 mm, 100 mm — matching common stud and frame widths Thicknesses: 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 15 mm, 20 mm Length: typically 100 mm A practical site kit carries 1 mm, 2 mm, 3 mm, 5 mm, and 10 mm packers — which combine to hit any required thickness from 1 mm to 20 mm+ without needing every possible size. Colour-coding by thickness (common in quality packer ranges) makes grabbing the right packer fast without measuring each piece. Precision Shims for Engineering Applications Beyond construction and routine machinery alignment, shims perform critical functions in precision engineering — applications where tolerances are tight and errors have direct mechanical consequences. Valve Train Shimming In overhead cam engines — common in modern diesel and petrol equipment — valve clearance (often called "tappet clearance" in the Australian trade) is set by selecting a shim disc of the correct thickness between the cam follower and the valve stem end. The clearance is measured with a feeler gauge at the specified temperature (usually cold), the existing shim is measured with a micrometer, and the correct replacement is selected from a range covering typically 2.5 mm to 3.5 mm in 0.025 mm steps. Incorrect valve clearance causes noisy valve operation (too much clearance) or poor valve closing and potential burning (too little). This is not a task where close is good enough — which is why valve shims are manufactured to tolerances of plus or minus 0.01 mm or better. Bearing Preload Tapered roller bearings in differentials, wheel hubs, and gearboxes require a specific preload — a controlled compressive force applied during assembly. Shims or collapsible spacers set this preload during build. Too little preload and the bearing runs loose, generating noise and heat. Too much and it overloads and overheats. Setting bearing preload requires proper measurement (rolling torque method) and correct shim selection — not a feel-based approximation. Hydraulic Relief Valve Pressure Setting Pressure relief valves in hydraulic circuits use a spring-loaded element set by shims between the spring end and the valve body. Adding shims raises the relief pressure; removing shims lowers it. Adjustments of 0.1 mm per shim can change the relief pressure by several bar — making this a precision shim application despite its straightforward appearance. Machine Tool Calibration and Fixturing In CNC and manual machining, shims adjust cutting tool heights, align workholding fixtures to a known datum, and compensate for tool variation in production jigs. Required adjustments are often in the 0.01–0.1 mm range — achievable with quality shim stock and proper measurement. Shimming is the standard production-floor method for fine calibration adjustments without the cost and time of machining. How to Choose the Right Shim Thickness Choosing the right shim thickness starts with measurement — not estimation, and not by trying shims until one fits. Here is the process for getting it right. Step 1: Measure the Gap For gaps under 1 mm: Use a feeler gauge (thickness gauge). A feeler gauge set provides blades from 0.05 mm to 1.0 mm or more. Insert blades until the correct thickness is found — the blade should slide through with light, consistent drag. Intermediate gaps are bridged by stacking two blades. For gaps over 1 mm: Use a digital vernier caliper for direct measurement, or a dial test indicator against a known datum. For machinery alignment: Laser alignment equipment measures offset and angularity at the coupling and calculates the exact correction required at each machine foot. Shim selection follows from this calculation — no manual gap measurement is needed in modern laser alignment work. Step 2: Select or Build the Thickness If a single shim at the measured thickness is available, use it. If not, stack shims to achieve the total. Keep the number of pieces to three or fewer. For example, a 0.375 mm gap can be filled with three 0.125 mm shims, or with one 0.25 mm plus one 0.125 mm — the two-piece stack is more stable and easier to handle. Step 3: Test Fit Before Final Assembly Fit the shim or stack into the gap before final torquing. The shim should slide in with slight resistance — not fall in freely (under-size) and not require force (over-size). A shim that must be hammered in is deforming the gap it is supposed to fill precisely. Once the fit is confirmed, torque to specification and re-check the measurement after torquing, as bolting can shift the shim position slightly. Common Thickness Sets to Stock For a typical industrial maintenance situation, stocking 0.025, 0.050, 0.075, 0.100, 0.125, 0.150, 0.200, 0.250, 0.500, and 1.000 mm gives the flexibility to hit almost any required thickness within 0.025 mm by stacking. A slotted alignment shim kit from AIMS covers the range needed for motor foot shimming in ready-to-use horseshoe form. Can You Stack Shims? (and How Many Is Too Many) Yes — stacking shims is entirely acceptable and is standard practice in alignment and gap-filling work. The question is where the practical limit lies and how to do it correctly. Why Stacking Works Quality shim stock is rolled to a known thickness within a tight tolerance. Stacking three 0.125 mm shims gives a total of 0.375 mm, and because each individual shim is accurate to plus or minus 0.003 mm, the cumulative error of the stack is plus or minus 0.009 mm — well within the tolerance of most alignment applications. The dimensional accuracy of a properly stacked shim assembly is entirely adequate for the tasks shims are used for. Where Stacking Causes Problems The limitation of stacking is physical, not dimensional. As the stack grows: The stack becomes less stable under vibration and can shift, particularly if individual shims are not held firmly by the clamping load Slotted shims become harder to insert cleanly as the stack thickness increases In corrosive environments, individual shims can corrode together, making future removal difficult The total number of loose pieces increases — more opportunities for pieces to fall, be mislabelled, or end up in the wrong position during reassembly The Practical Rule Three to four shims maximum in a single stack for alignment and precision work. For corrections exceeding 3–4 mm, use a machined spacer plate or a single thick steel shim rather than a tall stack of thin ones. For corrections under 0.3 mm, a single shim is always better than two if one is available at the right thickness. Stacking Best Practices Place thicker shims at the bottom and thinner shims on top — stable base, fine adjustment at the top Use the same alloy throughout the stack — mixing carbon steel and stainless can lead to galvanic corrosion bonding them together in wet environments In outdoor or corrosive environments, apply a thin coat of anti-seize between shims to prevent bonding Mark the thickness of each shim with a permanent marker before assembly — you will need that information at the next service Consider laminated shims as an alternative to loose stacks for applications requiring fine, repeatable adjustment Are Shims Structural? Load-Bearing Considerations Steel shims carrying structural loads is not unusual — it is the designed intent in many applications. Column base plates, machine mounting pads, and structural steel connections all routinely use steel shims as permanent load-carrying components. The question is whether the right material is selected and whether the application is within its limits. Steel Shims in Structural Applications Cold-rolled steel and stainless steel shims have high compressive strength — well above the bearing stresses typically encountered in structural base plate connections or machinery mounting. A stack of steel shims under a bolted base plate, properly installed and grouted, is a permanent structural element that carries the full column or machine load. For structural steel work in Australia, AS 4100 (Steel Structures) governs base plate connections. Where shims are specified, they should be structural-grade steel, sized to fully cover the bearing area, and grouted in position after the structure is aligned. Check with the structural engineer for specific shim size and material requirements — these will be in the drawings or engineer's notes. Machinery Mounting Loads Under an industrial motor or pump, the machine foot bears the combined static weight of the machine plus dynamic loads from vibration and torque reaction. For a properly installed, bolted-down machine, these loads are largely compressive — and steel shims handle compressive loads well. The shim stack should cover the full area of the machine foot where possible, distributing the load evenly rather than concentrating it. What Cannot Carry Structural Load Timber (cedar, pine, hardwood): Wood under sustained compressive load compresses, creeps, and deforms over time — meaning a machine that is correctly aligned today will be out of specification in six to twelve months. Timber also rots, swells with moisture, and provides no predictable compressive performance. Cedar shims are a legitimate tool for temporary positioning during installation; they are not a permanent solution in any structural or machinery application. Plastic packers under heavy machinery: HDPE construction packers are rated for construction-level loads in frame and window installation. They are not rated for the sustained compressive loads of industrial machinery. Do not substitute construction plastic packers for steel shims under motor feet, pump bases, or any heavy industrial equipment. Shims for Excavators and Heavy Equipment Heavy earthmoving equipment — excavators, loaders, bulldozers, cranes — uses shims in several critical locations. These are high-load, high-vibration, outdoor environments with mud, water, and aggressive conditions. The shims used here are thick, high-strength steel — nothing like the thin alignment shims used on electric motors. Excavator Pin Shimming Excavator buckets, arms, and booms connect via large-diameter steel pins running through bronze or steel bushes. As the bushes wear — under the constant loading and cycling of digging — lateral play develops at the pin joint. The bucket wiggles side-to-side in the boss rather than tracking straight, reducing dig accuracy, increasing loading on the pin and boss faces, and accelerating further wear in a self-worsening cycle. Steel shims take up this lateral play. The pin is removed, a shim of the appropriate thickness is fitted between the boss face and the machine structure on one or both sides, and the pin is refitted. The shim reduces total lateral clearance to within OEM specification — typically less than 1–2 mm for most excavators. Pin shims for this application are thick (typically 3–6 mm) and manufactured from high-strength steel to handle the side loads in the joint. Always check the OEM service manual for the specific machine and joint: maximum allowable play and the correct shimming procedure vary by machine model. Undercarriage Components Track tension on crawler equipment is adjusted via a hydraulic tensioner, but shims may be used during track reassembly and component replacement to set initial dimensions and compensate for worn components. Undercarriage shimming is a specialist task requiring knowledge of OEM service specifications. Structural Base Plates and Outrigger Support On mobile cranes, elevated work platforms, and other outrigger-supported equipment, base plate shimming may be used to level the machine on uneven ground before operation. These applications use thick steel shims or machined steel plates — not standard alignment shims. Load capacities are high, and correct support is critical for operational safety. How to Measure and Cut Shim Stock The ability to cut your own shim from stock is one of the most useful capabilities in a workshop. The process is simple, but the details matter for a result that is accurate, burr-free, and safe to handle. Measuring and Marking Mark the shim profile on the stock material using a fine-tip permanent marker or a scriber. For straight-edged shims, use a steel rule and scriber. For complex shapes, make a paper or cardboard template first, trace around it, then cut. For slotted shims, mark both the outer profile and the slot position carefully — the slot must align with the bolt centre. Measure twice, cut once. Cutting Methods by Thickness 0.025–0.100 mm (1–4 thou): Sharp scissors or shim-cutting scissors. At these thicknesses, the material cuts like thin metal foil. Handle carefully — the edges are sharp. 0.100–0.500 mm (4–20 thou): Aviation snips (compound action tin snips) for straight cuts, curves, and complex shapes. Left-hand and right-hand snips are available. Keep blades sharp — dull snips fold and buckle the edge rather than cutting clean. 0.500–1.500 mm (20–60 thou): Aviation snips for shorter cuts; a metal-cutting bandsaw for long straight cuts. Stainless steel in this range work-hardens quickly — a bandsaw is cleaner than snips. Over 1.5 mm: Metal-cutting bandsaw, angle grinder with cutting disc, or guillotine shear. Mark the cut line clearly, clamp the stock securely, and use eye and hand protection. Cutting the Slot in a Horseshoe Shim To cut the slot from flat stock for a horseshoe shim, use the drill-and-snip method: drill a clearance hole at the inner end of the slot (matching or slightly larger than the bolt diameter), then cut down both sides of the slot from the outer edge to the drilled hole using aviation snips. The drilled hole gives a clean radius at the inner end of the slot rather than a sharp corner, which can become a stress riser under repeated loading. Deburring Any cut edge on metal shim stock will have a burr. Deburr all cut edges before fitting — a burred edge will damage mating surfaces, prevent the shim from sitting flat, and is a laceration hazard during handling. Use a fine file, a deburring tool, or fine abrasive paper on a flat surface. For thin shim stock, draw a flat file lightly across the edge — one or two strokes is enough. Do not over-file. Marking Shims Before Assembly If the shim is going into an installation that will be disturbed in future — a motor that will need re-alignment, a base plate that may be lifted — mark the shim thickness with a permanent marker before assembly. When the machine comes apart at the next service, you know immediately what is in the stack without having to micrometer every piece. It takes ten seconds and saves significant time later. Common Questions About Industrial Shims What is an industrial shim used for? Industrial shims are thin precision spacers used to fill gaps, align machinery, adjust bearing preload, level baseplates and correct manufacturing tolerances. Common applications include aligning electric motors to pumps, levelling structural baseplates, setting bearing clearance in gearboxes, and adjusting cutting tool height in machining operations. They are made in graduated thicknesses from a few thousandths of a millimetre upwards. What's the difference between a shim and a washer? A washer distributes the clamping load of a fastener over a larger area to protect the surface beneath. A shim is a precision spacer used to fill a measured gap or adjust an alignment. Washers come in a few standard thicknesses for each diameter; shims come in many graduated thicknesses so you can stack them to achieve any required gap. They look similar but serve different purposes. What materials are shims made from? Common shim materials include stainless steel for general use, brass for electrical isolation and corrosion resistance, mild steel for non-critical work, aluminium for light-duty applications, and various plastics where electrical insulation or chemical resistance matters. Laminated shims are made up of layers that can be peeled off to fine-tune thickness without changing the part. How thick are industrial shims? Shims come in a wide range of thicknesses. Precision shims for machinery alignment start from very thin material and graduate upwards in fine increments — often in increments of a few hundredths of a millimetre at the thin end, stepping up to half-millimetre and one-millimetre sizes at the thicker end. Stacking shims of different thicknesses allows you to achieve almost any required gap. Where do you buy industrial shims? Industrial shims are stocked by industrial supply distributors who stock alignment, fastener and bearing maintenance product ranges. They are sold in pre-cut sizes, laminated peel-off forms, and as flat strips you cut to size on the job. For shaft alignment and motor-pump coupling work, slotted shims that slip under a baseplate without removing the fastener are the standard choice. AIMS Industrial stocks a range of industrial shims. Where to Buy Shims in Australia AIMS Industrial stocks a comprehensive range of precision shims and shim stock for Australian industrial, construction, and engineering applications. The range includes shim stock rolls and flat sheets in cold-rolled steel, stainless steel 304 and 316, and brass across a full range of thicknesses from 0.025 mm upward; slotted alignment shim kits for motor and machinery alignment work; plastic HDPE shim packers for construction framing, door, and window installation; and specialty shim products from Champion and Precision Brand. All products are available online with delivery to anywhere in Australia. For technical advice on material selection, thickness specification, or choosing the right shim format for a specific application, contact the AIMS Industrial team. Browse Shims & Shim Stock at AIMS Industrial → For GD&T symbols and their meanings under Australian and international standards, see our GD&T Symbols Guide. For dry and lubricated torque values across all common metric bolt grades, see our Metric Bolt Torque Chart.
Read moreCirclip Guide: Types, Sizes & Installation
A circlip is one of those fasteners that tradespeople handle dozens of times without ever stopping to think about what it actually is or how it works — until one flies across the workshop and disappears under the bench. This guide covers everything you need to know: the different types, how to read a size chart, which pliers to use, and how to install and remove them correctly the first time. Types of Circlips — Quick Reference Internal and external are the primary categories, but within those categories there are several distinct construction types. The type determines groove compatibility, installation method, and performance characteristics. Type Installation direction Plier holes Groove profile Typical load Standard external (DIN 471) Axial Yes DIN 471 tapered shoulder Medium–high Standard internal (DIN 472) Axial Yes DIN 472 tapered shoulder Medium–high E-clip Radial (side-on) No Simple circumferential groove Light–medium Bowed circlip Axial Yes DIN 471/472 (wider groove) Medium (preload) Wire circlip Axial No Round-bottomed groove Light–medium Heavy-duty Axial Yes Heavy-duty DIN variant High What Is a Circlip? A circlip — also called a snap ring, retaining ring, or C-clip — is a semi-flexible, open-ended metal ring that snaps into a machined groove on a shaft or inside a bore. Once seated, it acts as a mechanical shoulder: it allows rotation but prevents axial movement, stopping components from sliding along the shaft or out of the housing. The core mechanism is simple. The ring is manufactured slightly smaller (for external clips) or slightly larger (for internal clips) than the groove it sits in. To install it, you deform the ring elastically — opening it to pass over a shaft, or closing it to fit inside a bore — then release it into the groove. The ring springs back toward its natural diameter, gripping the groove walls. The groove geometry (depth, width, and shoulder profile) determines how much axial load the circlip can resist. The name "circlip" is a portmanteau of "circle" and "clip," and has become the standard Australian and British term for this fastener family. The American equivalent term is "snap ring" or "retaining ring." You will also encounter the term "Jesus clip" — a workshop colloquialism that refers to the circlip's tendency to launch itself at high velocity when being removed with pliers, prompting the inevitable exclamation when it disappears. This is not merely humorous: a releasing circlip under spring tension can travel several metres and cause eye injury. Safety glasses are not optional. Internal vs External Circlips The single most important distinction in circlips is whether the clip is internal or external. Getting this wrong means you are looking at a component that physically cannot be installed. External Circlips An external circlip fits around a shaft, seating in a groove machined into the shaft's outer diameter. To install it, you expand (open) the clip using external circlip pliers, pass it over the shaft to the groove position, and release. The clip springs closed into the groove. The clip's outer surface sits proud of the shaft OD, creating a shoulder that retains whatever component is loaded onto the shaft — a bearing, gear, pulley, or collar. External circlips are the type you encounter most often in shaft-and-hub assemblies. They stop components from migrating along a shaft toward an open end. On a wheel hub, for example, an external circlip retains the bearing in its axial position. On a conveyor roller shaft, external circlips hold the roller body in place between two flanges. Internal Circlips An internal circlip fits inside a bore or housing, seating in a groove machined into the bore's inner diameter. To install it, you compress (close) the clip using internal circlip pliers, guide it into the bore to the groove position, and release. The clip springs open into the groove. The clip's inner surface now sits proud of the bore ID, creating a shoulder that retains whatever component sits inside the bore — a bearing outer race, bushing, or pin. Internal circlips are standard in bearing housings and gear housings. The bearing's outer race is pressed into the bore, and the internal circlip prevents it from being pushed axially through the housing under load. How to Tell Which You Have If you are looking at an existing assembly and need to identify the clip type: an external circlip is visible around the outside of a shaft, with the lugs (plier holes) pointing radially outward. An internal circlip is recessed inside a bore, visible when looking into the opening, with lugs pointing inward toward the bore centreline. If you are selecting from scratch, the rule is: shaft groove → external clip, bore groove → internal clip. Types of Circlips Internal and external are the primary categories, but within those categories there are several distinct construction types. The type determines groove compatibility, installation method, and performance characteristics. Standard Stamped Circlip (DIN 471 / DIN 472) The most common type. Stamped from flat spring steel strip, these have a tapered cross-section (thicker at the outer radius for external, thicker at the inner radius for internal) with two lugs and plier holes for installation and removal. The tapered section locks into the groove's angled shoulder under axial load — the harder the clip is pushed, the tighter it wedges into the groove. DIN 471 is the standard for external clips; DIN 472 for internal. When someone says "circlip" without qualification, this is what they mean. E-Clip (E-Ring) An E-clip is installed radially — from the side — rather than axially. The groove for an E-clip is a simple circumferential groove without the tapered shoulder of a DIN 471/472 groove. The clip has an E-shaped cross-section: a central spine with three prongs that grip the groove. You push it onto the shaft from the side until it snaps into the groove; no pliers required, though a flat-bladed screwdriver or punch is often used. E-clips are used where axial installation is impossible — for example, on a pin that is captive in an assembly and cannot have components slid over the end. They are common in light to medium-duty applications: lawn equipment, conveyor systems, light industrial machinery. They are not rated for high axial loads — the three-point contact provides considerably less retention force than a full DIN-style circlip in a tapered groove. Bowed (Dished) Circlip A bowed circlip is stamped with a deliberate axial bow — when viewed from the side, the ring is slightly curved rather than flat. When installed, this bow is partially compressed, and the spring-back force applies a continuous axial preload to the retained component. This takes up end-float (axial play) in an assembly, preventing the component from rattling or fretting in its groove. Bowed circlips are used in precision bearing applications, instrument mechanisms, and anywhere that controlled end-float or preload is required. The standard flat circlip allows the retained component to move axially within the groove clearance; the bowed circlip eliminates that play. Wire Circlip A wire circlip is bent from round-section wire rather than stamped from flat strip. The circular cross-section means it requires a different groove profile — specifically a round-bottomed or semicircular groove, not the flat-bottomed tapered groove of a DIN 471/472 clip. This is a critical compatibility point. Wire circlips and stamped circlips are not interchangeable in the same groove. A stamped DIN circlip installed in a wire-groove, or a wire circlip installed in a DIN tapered groove, will not seat correctly and will fail under load. If you are replacing a wire circlip, verify the groove profile before ordering. Wire circlips are used in piston pin (wrist pin) applications in two-stroke and four-stroke engines, where the small bore diameter and the need for a low-profile clip favour the wire construction. Heavy-Duty / Reinforced Circlip Heavy-duty circlips are manufactured to tighter tolerances from higher-grade spring steel, with increased section thickness for higher axial load capacity. They follow DIN 471/472 groove profiles but are not interchangeable with standard clips — groove dimensions for heavy-duty clips differ. Specify by load rating, not just nominal size. Type Installation direction Plier holes Groove profile Typical load Standard external (DIN 471) Axial Yes DIN 471 tapered shoulder Medium–high Standard internal (DIN 472) Axial Yes DIN 472 tapered shoulder Medium–high E-clip Radial (side-on) No Simple circumferential groove Light–medium Bowed circlip Axial Yes DIN 471/472 (wider groove) Medium (preload) Wire circlip Axial No Round-bottomed groove Light–medium Heavy-duty Axial Yes Heavy-duty DIN variant High Circlip Materials The material determines the circlip's corrosion resistance, operating temperature range, and suitability for specific environments. Most industrial circlips are spring steel, but several alternatives exist for specialised applications. Spring Steel (Carbon Steel) The standard material for the vast majority of industrial and automotive circlips. Carbon steel is heat-treated and tempered to give the combination of high yield strength (to resist permanent deformation under load) and adequate ductility (to allow elastic deformation during installation without cracking). Hardness is typically 47–52 HRC. Spring steel circlips are supplied either self-colour (plain steel, no surface treatment) or zinc-plated for basic atmospheric corrosion protection. Self-colour clips are suitable for enclosed, lubricated applications — inside gearboxes, sealed bearing housings, engine components. Zinc-plated clips are adequate for mild workshop environments. Neither is appropriate for wet, chemical, or outdoor exposure. Stainless Steel (304 and 316) Stainless circlips are specified for corrosive environments: food processing equipment, marine and coastal installations, wash-down areas, and outdoor plant. The trade-off is reduced spring hardness compared to carbon steel — stainless spring material is softer, which reduces the maximum axial load rating for a given size compared to the carbon steel equivalent. Select 304 stainless for general atmospheric and mild corrosive environments. Specify 316 stainless for chloride-rich exposure — coastal salt spray, CIP cleaning with chlorinated solutions, marine immersion. Do not assume 304 is adequate for a coastal Queensland installation; the chloride content of coastal air is sufficient to cause pitting on 304 over time. Phosphor Bronze Phosphor bronze circlips are used in hazardous-area equipment and electrical applications. Bronze has low spark-generation risk on impact (non-ferrous), making it appropriate for use near flammable or explosive atmospheres. It also has good electrical conductivity and is used where galvanic compatibility with other copper-alloy components is required. Not a common stocked item — typically a special-order material. Beryllium Copper Very high conductivity and good spring properties. Used in precision electrical connectors and instrument assemblies. Not generally available in standard DIN circlip profiles — a specialist item for specific applications. Standards — DIN 471 and DIN 472 The two standards you will encounter on most circlip packaging and engineering drawings in Australia are DIN 471 and DIN 472. Both are German Industrial Standards (Deutsche Industrie Norm) that have become the de facto international standard for metric stamped circlips. DIN 471 specifies external circlips for shafts. The nominal size equals the shaft diameter in millimetres. A DIN 471 – 25 circlip is for a 25mm shaft. The standard specifies the circlip's free diameter, section thickness, section height, and the corresponding groove dimensions (groove diameter, groove width, and groove corner radius) that the shaft must be machined to. DIN 472 specifies internal circlips for bores. The nominal size equals the bore diameter in millimetres. A DIN 472 – 52 circlip is for a 52mm bore. The standard specifies the same parameters as DIN 471 but for bore grooves. The groove dimensions in these standards are not arbitrary — the tapered shoulder and groove depth are designed so that the clip's bevelled inner face engages the groove shoulder under axial load, increasing the effective retention force. If the groove is cut to incorrect dimensions, the clip will either fall out (groove too wide or too shallow) or not seat fully (groove too narrow or too deep). Other standards you may encounter: JIS B 2804 (Japanese standard, dimensionally similar to DIN 471/472 for most sizes), BS 3673 (British standard, now largely superseded by DIN in practice). Imperial-size circlips are available for equipment manufactured to inch standards — these are specified by shaft/bore diameter in fractional inches and follow their own groove dimension tables. Circlip Sizes — How to Measure and Order The most common ordering error is measuring the wrong dimension. Here is the correct approach. For External Circlips (DIN 471) Measure the shaft diameter. The nominal circlip size equals the shaft diameter. Do not measure the groove — the groove dimensions are specified by the standard and derived from the shaft diameter. If the shaft is 20mm, you need a DIN 471 – 20 circlip. If you are replacing an existing circlip and the shaft groove is already cut, you can verify the shaft diameter from the groove itself: the shaft nominal diameter equals the groove diameter plus twice the groove depth (approximately), but measuring the shaft directly away from the groove is simpler and more accurate. For Internal Circlips (DIN 472) Measure the bore diameter. The nominal circlip size equals the bore diameter. A 40mm bore takes a DIN 472 – 40 circlip. Do not measure the groove ID. External Circlip Reference Table (DIN 471 — Selected Metric Sizes) Shaft Ø (mm) Groove Ø d2 (mm) Groove Width b (mm) Circlip Thickness s (mm) Circlip Free Ø (approx mm) 8 7.4 0.9 0.8 7.1 10 9.3 1.1 1.0 9.0 12 11.0 1.1 1.0 10.5 15 14.1 1.1 1.0 13.8 17 16.2 1.1 1.0 15.7 20 18.5 1.3 1.2 18.1 25 23.2 1.3 1.2 22.9 30 27.9 1.5 1.5 27.6 35 32.2 1.7 1.5 31.5 40 37.0 1.7 1.75 36.5 45 42.0 1.7 1.75 41.5 50 47.0 2.0 2.0 46.0 55 51.5 2.0 2.0 50.5 60 56.5 2.0 2.0 55.5 70 65.5 2.5 2.5 64.0 80 74.5 2.5 2.5 74.0 100 93.5 3.0 3.0 93.0 Internal Circlip Reference Table (DIN 472 — Selected Metric Sizes) Bore Ø (mm) Groove Ø d2 (mm) Groove Width b (mm) Circlip Thickness s (mm) Circlip Free Ø (approx mm) 10 10.8 1.0 0.8 11.2 12 13.0 1.1 1.0 13.4 15 16.2 1.1 1.0 16.8 17 18.2 1.1 1.0 18.8 20 21.5 1.3 1.2 22.2 25 26.6 1.3 1.2 27.2 30 32.1 1.5 1.5 32.8 35 37.8 1.7 1.5 38.5 40 43.5 1.7 1.75 44.0 45 48.5 1.7 1.75 49.0 50 54.0 2.0 2.0 54.5 55 59.0 2.0 2.0 59.5 60 64.0 2.0 2.0 65.0 70 74.5 2.5 2.5 75.5 80 85.0 2.5 2.5 86.0 100 106.0 3.0 3.0 107.0 Dimensions are indicative for standard spring steel circlips. Always verify against the manufacturer's catalogue or DIN standard tables for critical applications. Imperial Circlips Imperial circlips are available for equipment manufactured to inch standards — older British-heritage machinery, American-specification plant, and some agricultural equipment. Imperial sizes are specified by shaft or bore diameter in fractional or decimal inches (e.g., ½", ¾", 1", 1¼"). The groove dimensions follow their own tables and are not interchangeable with metric grooves at nominally similar diameters. When ordering imperial circlips, specify both the nominal diameter and the standard (e.g., ½" external, AS circlip or DIN 471 equivalent in imperial). Circlip Pliers — Types and Selection "Circlip pliers" at 2,100 searches per month in Australia — more than "circlip" itself — tells you something: the pliers are frequently the blocker. Using the wrong plier type, or using pliers with tips that don't fit the clip, causes most of the installation problems, including the "Jesus clip" launch event. The Four Basic Types Internal straight: Tips point directly forward, parallel to the handles. When the handles are squeezed, the tips move together — compressing the clip. Used for internal circlips in bores where there is clear axial access. The straight configuration gives the best control for accessible bores and larger sizes. Internal bent (angled tips): Tips are angled — typically at 45° or 90° — relative to the handles. The compress-on-squeeze action is the same as internal straight, but the angle allows access to bores that are recessed, at the bottom of a counterbore, or otherwise obstructed. If you find yourself twisting your wrist awkwardly with straight pliers, bent tips are the answer. External straight: Tips point forward and the action is reversed — squeezing the handles moves the tips apart, expanding the clip. Used for external circlips on shafts with clear access. The most common type for general shaft work. External bent (angled tips): Same expand-on-squeeze action, angled tips for restricted access. Used when the shaft groove is close to a housing face, deep in an assembly, or otherwise difficult to approach axially. Combination and Reversible Pliers Combination circlip pliers can be configured for either internal or external use by reversing the plier tips or switching between tip sets. These are useful for a general workshop where both internal and external clips are handled, and where the volume of circlip work does not justify a full set of dedicated pliers. The trade-off is slightly more setup time when switching between types and occasionally less ergonomic feel than a dedicated plier. Knipex is the benchmark for quality circlip pliers in the Australian trade market — their 4-piece and 8-piece circlip plier sets cover the common size ranges and configurations. For a general maintenance fitter, a 4-piece set (internal straight, internal bent, external straight, external bent) in the 19–60mm range covers most everyday applications. Tip Size and Fit Circlip pliers come in different size ranges because the plier holes in the clip vary with clip size. The key rule: the tip must fit the plier hole fully. A tip that is too large cannot enter the hole. A tip that is too small enters but doesn't engage the hole wall — under spring tension, the tip slips out and the clip launches. Most quality circlip pliers include interchangeable tips of different diameters to cover a range of clip sizes. When selecting a set, check that the stated size range covers the clips you are working with. Small engine circlips (8–12mm shaft) require finer tips than industrial bearing clips (40–100mm). Plier type Handle action Tip action Use case Internal straight Squeeze Tips move together (compress) Internal circlips, open access Internal bent Squeeze Tips move together (compress) Internal circlips, restricted/recessed bores External straight Squeeze Tips move apart (expand) External circlips, open access External bent Squeeze Tips move apart (expand) External circlips, restricted/deep shaft access Combination / reversible Squeeze Configurable General workshop, both clip types How to Install a Circlip Correctly Correct installation has three components: using the right pliers with fully-seated tips, installing the clip the right way around, and verifying the clip is fully seated in the groove. Missing any one of these causes failures that range from annoying (clip falls out during assembly) to hazardous (clip ejects under load in service). Which Way Round Does a Circlip Go? This is the question most articles skip, and it is the second-most-common installation error after wrong plier size. Stamped circlips have two distinct sides that result from the manufacturing process: Smooth/chamfered side: The side from which the stamping die entered the metal. This side has a slight chamfer on the inner radius of the clip. This is the load-bearing side. Burr/flat side: The underside of the stamp. This side has slight raised edges (burr) and a square inner edge. This side faces away from the retained component. The smooth chamfered side must face the retained component — that is, the side that contacts the component being held against the clip. The reason matters: the groove in the shaft or bore has a matching tapered shoulder. When axial load is applied, the clip's chamfered face bears against the groove's tapered shoulder. The chamfer-to-taper contact geometry causes the clip to wedge tighter into the groove the harder it is pushed — self-reinforcing retention. If the clip is installed reversed (flat/burr side toward the component), the flat edge bears against the rounded groove shoulder. Under axial load, the flat edge bites into the groove wall, the clip deforms, and it can ride up the chamfer and eject from the groove. This failure mechanism is responsible for a significant proportion of circlip field failures and is entirely preventable by installing the clip the right way around. Installing an External Circlip (Step by Step) Put on safety glasses. Position a cloth or your free hand to cover the clip during the final installation — this contains the clip if it slips from the pliers. Select external circlip pliers of the correct size range for the clip. Check the tip diameter fits the plier holes fully — tips should enter without force and without visible play. Hold the clip with the smooth (chamfered) face toward you. The smooth face will face the retained component, which is between the clip and the shaft shoulder. Seat both plier tips fully into the plier holes. Both tips must be fully engaged before you apply any opening force. Squeeze the handles to expand the clip. Expand only as far as needed to pass over the shaft — over-expansion permanently deforms the clip and reduces retention force. With the clip expanded, slide it along the shaft to the groove position. Keep the clip square to the shaft axis — do not tilt. Release the handles slowly, allowing the clip to spring closed into the groove. Remove the pliers and check the clip is fully seated: run a fingernail or a flat probe around the entire circumference of the clip. The clip must sit flat and flush in the groove with no section standing proud. If any section is proud, the clip is not fully engaged — do not proceed. Partially seated circlips can eject under load with no warning. Installing an Internal Circlip (Step by Step) Safety glasses on. Select internal circlip pliers of the correct size. Verify tip fit in the plier holes. Orient the clip with the smooth (chamfered) face pointing toward the retained component (into the bore). Seat both tips fully in the plier holes. Squeeze to compress the clip until it is smaller than the bore diameter. Guide the compressed clip into the bore, keeping it square to the bore axis. Do not tilt — a tilted clip can scratch the bore surface or spring into the bore in an uncontrolled manner. Position the clip over the groove location and release the handles slowly. The clip will spring open into the groove. Check seating — run a probe around the full inner circumference. The clip must sit flat in the groove, fully engaged around the entire perimeter. Installing an E-Clip E-clips do not require dedicated pliers. Hold the clip over the shaft groove (the shaft must be horizontal or supported). Position the central prong of the E over the groove. Press the clip onto the shaft with a flat-bladed screwdriver or a suitable punch, pushing firmly until the three prongs snap into the groove. Verify by trying to slide the clip axially — it should not move. Remove with a small flat screwdriver by levering one prong out of the groove. How to Remove a Circlip Removal is essentially installation in reverse, but with two additional considerations: the clip has been in service and may be corroded or deformed, and the clip should generally be replaced rather than reinstalled. Standard Removal Use the same plier type and tip-fit rules as for installation. For external circlips, expand the clip to clear the shaft diameter and slide it off. For internal circlips, compress the clip and withdraw it from the bore. Cover the clip as it releases — at the moment it clears the shaft or bore edge, the spring energy releases and the clip can launch. Stuck or Corroded Circlips A circlip that has been in a corrosive environment or has not been removed for years may be seized in the groove by rust or contamination. The approach: Apply penetrating oil to the clip and groove. Allow a minimum of 10–15 minutes for penetration; longer for heavily corroded assemblies. Applying heat to the shaft or housing to expand the metal slightly, then allowing it to cool while the penetrating oil wicks in, significantly increases success rate on seized clips. Re-attempt with circlip pliers, applying steady force rather than jerky leverage. Jerky force on a corroded clip is more likely to deform the plier holes and leave you with no purchase. If the plier holes are damaged or obscured by corrosion, use two small flat-bladed screwdrivers — one at each ear of the clip — to pry it open (external) or closed (internal) simultaneously. This requires steadiness and eye protection. As a last resort on an external circlip, a thin cold chisel driven carefully under the clip's outer edge can start it out of the groove. This damages the groove surface and should only be used when the clip will not be reinstalled and the groove condition does not matter. Removal Without Pliers This is the emergency method — not the recommended method. For external circlips: use two small flat-bladed screwdrivers, one at each ear, to lever the clip open until it clears the shaft. The risk is clip ejection (cover with a rag) and tip-hole damage that may prevent re-installation if the clip needs to be reused. For internal circlips: two fine screwdrivers levering toward the centre to compress the clip into the bore. A pair of needle-nose pliers can substitute for internal circlip pliers in a genuine emergency — insert the tips into the plier holes and squeeze. The geometry is wrong (needle-nose tips are parallel, not angled inward like internal pliers) but it works for larger clips in accessible bores. It does not work well for small clips or restricted access. Should You Reuse a Circlip After Removal? The technically correct answer is: a circlip can be reused if it is undamaged and has not been permanently deformed. In practice, for most applications the correct answer is: replace it. Here is the reasoning. Every time a circlip is expanded or compressed for installation or removal, it is deformed elastically. If the deformation stays below the yield point, the clip returns to its original geometry and retains its spring force. However, repeated cycles — or even a single cycle where the clip was over-expanded or over-compressed — can cause permanent deformation: the plier holes elongate, the ring develops a slightly enlarged diameter, or the section loses some springiness. A clip with even modest permanent deformation has reduced retention force compared to a new clip. For non-critical applications (handle pivot pins, light covers, low-load assemblies), a circlip that passes visual inspection — no cracks, plier holes intact, ring sits flat without visible distortion — can reasonably be reused. For critical applications — engine piston pins, transmission shaft retention, bearing housing retention in load-bearing equipment — replace on every disassembly. The cost of a circlip is negligible. The cost of a retained component migrating because of a fatigued circlip is not. Signs a circlip should be replaced: Visible cracks anywhere in the ring Plier holes deformed, elongated, or enlarged Ring does not sit flat (permanent bow in a non-bowed clip) Visible corrosion pitting, especially at the plier holes or inner radius Ring diameter visibly larger (external) or smaller (internal) than a new equivalent Any clip that had to be forced during removal — it has absorbed the force as deformation Common Mistakes When Working With Circlips These are the errors that account for the majority of circlip installation failures, field ejections, and injuries: Wrong Plier Type Using internal pliers on an external clip (or vice versa) results in the tip action working against you — you are trying to expand while the pliers compress, or vice versa. The clip fights you, you apply more force, and the clip launches when it eventually slips. Internal and external are not interchangeable. Check the plier type before you start. Tips Not Fully Seated Partially inserted tips — resting on the rim of the plier hole rather than fully through it — have a point contact with the clip rather than a face contact. Under spring force, the tip slides off the hole edge and the clip releases suddenly. Seat tips fully, every time. Feel them bottom out before applying opening or closing force. Installed Backwards As described in the installation section: smooth/chamfered face toward the retained component. A reversed circlip can appear to seat correctly and may hold initially. Under cyclic axial load, the ejection mechanism described above eventually triggers. If a circlip in a known-good groove is failing repeatedly, check orientation before assuming it is the wrong size. Wrong Size A clip that is one size too large fits loosely in the groove and can rattle out or be pushed out under low axial load. A clip that is one size too small cannot be fully seated in the groove. Both are dangerous. Measure the shaft or bore diameter — do not guess, and do not reuse packaging from a previous clip if you are not certain it was the right size to begin with. Over-Expanding or Over-Compressing Opening an external clip only as far as needed to clear the shaft, then releasing — not expanding it wide and slamming it down. Excessive deformation during installation is permanent. Clips that have been over-worked feel loose in the groove even when nominally the correct size. Use the minimum deformation necessary. Mixing Metric and Imperial A 20mm shaft and a ¾" shaft (19.05mm) are close enough in diameter that a clip from one system may appear to fit the other's groove — and it will, loosely. This is a groove mismatch, not just a size mismatch. The groove profile for a metric DIN 471 – 20 clip is not the same as the groove profile for a ¾" imperial clip, so the clip will not fully engage the groove shoulder even if it appears seated. Always confirm metric vs imperial before ordering. Not Checking Seating After Installation Visual inspection from above is not sufficient. Run a fingernail or a probe around the full circumference of the clip after installation. A clip that is fully seated sits flush in the groove with no section proud. A section that has jumped the groove edge looks seated from above but is sitting on the groove shoulder rather than in it — and it will eject as soon as any axial load is applied. Common Applications Circlips are found in nearly every mechanical assembly that involves rotating shafts, linear motion components, or pinned joints. These are the most common contexts an Australian maintenance fitter will encounter them: Automotive and Vehicle Piston pin (wrist pin) retention in petrol and diesel engines is one of the highest-volume circlip applications — wire circlips retain the piston pin from migrating axially through the piston bosses. Gearbox and transmission assemblies use circlips extensively: shaft retention, gear and synchroniser hub positioning, output shaft bearing retention. CV joints and axle shafts use circlips to retain the joint to the shaft. Wheel hub bearing retention — both inner bearing retention in the hub and outer retention in the knuckle — frequently uses external and internal circlips. Brake caliper pin retention and ABS sensor ring retention are further examples. Industrial Bearings and Shafts The largest category by part count in a typical industrial maintenance environment. External circlips retain bearings on shafts in conveyor rollers, pump shafts, gear reducers, agitators, and fan assemblies. Internal circlips retain bearing outer races in housings — the bearing is pressed into the housing bore and the circlip prevents it from being pushed axially through under load. Shaft collars and sprocket hubs are frequently retained by external circlips rather than set screws in lower-load applications. Hydraulic and Pneumatic Cylinders Piston rod retention within the cylinder barrel, and end-cap retention in some cylinder designs, uses internal circlips. These are safety-critical: the circlip is the sole mechanism preventing the piston rod assembly from being expelled from the cylinder under hydraulic pressure. Specification, groove condition, and clip condition must be to manufacturer's requirements. Tools and Equipment Angle grinder guard retention, drill chuck retention, impact driver anvil retention, and handle pivot assemblies in hand tools all use circlips. These are generally E-clips or standard external clips in smaller sizes (8–20mm range). A maintenance fitter disassembling a tool for a gear or bearing replacement will encounter these routinely. Electric Motors Bearing retention at both drive-end and non-drive-end of electric motors uses internal and external circlips in the end-shield bores and on the shaft respectively. When reconditioning motors, these clips should be replaced as a matter of course — the cost is trivial relative to the labour in the bearing replacement. Agricultural and Mining Equipment Pin and clevis joints in agricultural equipment (linkage pins on implements, PTO shaft joints, harvester components) use E-clips and external circlips for pin retention. Mining equipment — conveyor systems, screens, crushers — uses larger-format circlips in bearing housings and shaft retention. For high-vibration mining applications, circlip selection and groove condition are particularly important; vibration is the enemy of an incorrectly seated or undersized circlip. Frequently Asked Questions What is a circlip? A circlip is a semi-flexible, open-ended metal ring that snaps into a machined groove on a shaft or inside a bore to prevent axial movement while allowing rotation. It creates a mechanical shoulder — a stop — that retains components in their axial position. Circlips are one of the most compact and cost-effective fastening methods for shaft and bore assemblies, requiring no threading, no adhesives, and no welding. They are removable and reusable (with limitations) and can be installed and removed with the correct pliers in seconds. What is the difference between a circlip and a snap ring? Nothing practical. They are the same fastener. "Circlip" is the Australian and British term; "snap ring" is the American term. "Retaining ring" is the broader generic category that includes circlips but also other ring-style retainers. "C-clip" is a colloquial alternative. In Australian industrial supply, you will typically find them catalogued as circlips. American machinery documentation will call them snap rings. If someone asks for a snap ring and gives you a shaft diameter, order a circlip of the same nominal size — they are dimensionally equivalent. What is the difference between internal and external circlips? An external circlip fits around a shaft, in a groove on the shaft's outer diameter. An internal circlip fits inside a bore, in a groove on the bore's inner diameter. They require different pliers — external pliers expand the clip to pass over the shaft; internal pliers compress the clip to fit inside the bore. They are not interchangeable: an external clip cannot function as an internal clip and vice versa, as the groove profiles, nominal size references, and retention geometry are all different. What is an E-clip? An E-clip (also called an E-ring or push-on clip) is installed radially from the side of the shaft rather than axially over the end. It has an E-shaped cross-section with a central spine and three prongs that grip a simple circumferential groove on the shaft. No pliers are required — the clip is pushed onto the shaft from the side until it snaps into the groove. E-clips are used where axial installation is impossible (the shaft is captive in an assembly with no access from the end) and in lighter-duty applications where the full retention force of a standard DIN circlip is not required. Which way round does a circlip go? The smooth (chamfered) side faces the retained component. Stamped circlips have a smooth chamfered side and a flat burred side as a result of the stamping process. The chamfered inner edge of the smooth side engages the angled shoulder of the groove under axial load, wedging the clip tighter the harder it is pushed. If installed reversed (flat side toward the component), the flat edge bears against the groove shoulder and can ride up under load, eventually ejecting the clip. If a circlip is failing in a correct groove, check orientation before assuming size is the problem. How do you measure what size circlip you need? For an external circlip (on a shaft): measure the shaft diameter. The nominal circlip size equals the shaft diameter in millimetres. For an internal circlip (in a bore): measure the bore diameter. The nominal size equals the bore diameter in millimetres. Do not measure the groove — the groove dimensions are derived from the shaft or bore diameter in the DIN 471/472 standard tables. If you are unsure of the shaft or bore size, measure it directly with a calliper rather than trying to measure the groove or the old clip. Can you install a circlip without pliers? In an emergency, yes — but it is not recommended. External circlips can be expanded over a shaft using two flat-bladed screwdrivers, one at each ear, levering outward simultaneously. The risks are high: the clip can launch from the screwdrivers, the plier holes can be damaged, and without control over the expansion the clip is easily over-deformed. Internal clips are harder to compress without dedicated pliers. If you regularly work with circlips, a basic four-piece plier set is a one-time investment that prevents the frustration, the risk, and the lost clips. Why does my circlip keep coming out of its groove? Four causes, in rough order of frequency: (1) Clip installed backwards — flat side toward the component; the ejection mechanism described above is triggered under axial load. (2) Clip not fully seated — one section has jumped the groove shoulder and appears seated but is resting on the groove face. (3) Wrong size — a clip one size too large sits loosely in the groove and can be displaced by vibration or low axial loads. (4) Groove damage or wear — a groove that has been burred, worn wide, or has an incorrect shoulder angle will not retain the clip correctly. Check orientation first, then seating, then size, then groove condition. Can you reuse a circlip after removing it? For non-critical applications, yes — if the clip passes inspection: no cracks, plier holes intact, ring sits flat, no permanent enlargement (external) or reduction (internal) of diameter. For critical applications — engine components, transmission shafts, load-bearing bearing retention, hydraulic cylinders — replace on every disassembly. A circlip costs cents; the consequences of a retained-component failure in a critical assembly are significantly more expensive and potentially unsafe. What is the difference between DIN 471 and DIN 472? DIN 471 specifies external circlips for shafts. DIN 472 specifies internal circlips for bores. Both are German Industrial Standards that define the clip geometry, material requirements, and the groove dimensions that the shaft or bore must be machined to. The nominal size in DIN 471 is the shaft diameter; in DIN 472, it is the bore diameter. A component marked "DIN 471 – 25" is an external circlip for a 25mm shaft. A component marked "DIN 472 – 52" is an internal circlip for a 52mm bore. What material should I use for my circlip in a corrosive environment? Stainless steel. For general corrosive environments and mild coastal exposure, 304 stainless is adequate. For chloride-rich environments — direct coastal exposure, marine installations, salt spray, or wash-down with chlorinated cleaning agents — specify 316 stainless. For food processing applications where both corrosion resistance and hygiene standards apply, 316 stainless is standard. Zinc-plated spring steel is suitable for enclosed, protected environments (inside a sealed gearbox or housing) but not for wet or outdoor exposure. Standard self-colour spring steel should not be used in any environment where moisture contact is expected. What is the difference between circlip pliers and snap ring pliers? Nothing — they are the same tool. "Circlip pliers" is the Australian and British term; "snap ring pliers" is the American term. In practice both refer to the same family of tools: internal straight, internal bent, external straight, external bent, and combination types. If you search for "snap ring pliers" in an Australian tool catalogue you will typically be redirected to or find the same products listed as circlip pliers. The selection criteria — internal vs external, straight vs bent, tip size range — are identical regardless of the name used. Shop Circlips at AIMS Industrial AIMS Industrial stocks internal and external circlips across a full range of metric sizes in spring steel (self-colour and zinc-plated) and stainless steel. E-clips, circlip plier sets, and assorted circlip kits also available. Shop Circlips & Snap Rings Our Metric Bolt Torque Chart lists tightening torque in Nm for every common metric bolt size and grade. People Also Ask — Circlips Q: What is the difference between an internal and external circlip? An internal circlip (also called an inward-acting snap ring) fits into a groove machined inside a bore and retains a shaft or bearing within the bore. The open ends face inward toward the shaft centre. An external circlip fits into a groove machined on the outside surface of a shaft and retains a component on the shaft. The open ends face outward. The pliers required are also different — internal circlip pliers open the ring to fit into the bore; external circlip pliers close the ring to fit onto the shaft. Q: What tool do I need to install and remove circlips? Circlip pliers are required — attempting to install or remove circlips with screwdrivers or needle-nose pliers risks sudden release and dangerous projection of the ring. Internal circlip pliers have outward-pointing tips that expand when the handles are squeezed. External circlip pliers have inward-pointing tips that close when handles are squeezed. Both types are available in straight or 90° offset tip configurations for access in confined spaces. Always point the circlip away from yourself and others when releasing tension. Q: Can a circlip be reused after removal? Single-use circlips must be discarded after removal — once deformed by the installation and removal cycle, their retention force is reduced and they may not seat correctly in the groove. Many manufacturers specify circlips as non-reusable. Standard DIN circlips for general maintenance purposes are often reused in practice if they show no deformation, but this is at the maintainer's discretion. For safety-critical applications such as brake caliper pins, wheel bearings and drive shafts, always fit new circlips on reassembly. Q: What standards cover circlip dimensions? Circlip dimensions are covered primarily by DIN 471 (external circlips for shafts), DIN 472 (internal circlips for bores) and the equivalent ISO 9633 for external and ISO 9626 for internal. These standards specify the nominal diameter, wire diameter, groove dimensions and material properties. When ordering replacement circlips, specifying the DIN number and nominal shaft or bore diameter ensures the correct component. AIMS stocks DIN 471 and DIN 472 circlips across the common industrial diameter range. Q: Why would a circlip fail or come loose in service? Circlip failures have three main causes. First, incorrect groove dimensions — if the groove is too wide, the circlip can rotate and work out; if too shallow, it does not fully seat. Second, incorrect circlip selection — a circlip for a smaller shaft forced into a larger groove has inadequate retention force. Third, fatigue from repeated axial loading cycles eventually fatigues the ring material. High-vibration applications may require heavier section circlips or alternative retention methods such as cotter pins or bolt-through retainers. Pair this with the right axial bearing — see the AIMS thrust bearings collection. For o-rings and o-ring kits, see our o-rings and o-ring kits range stocked across Australia.
Read moregrub-screw-guide
Socket set screws — called grub screws in most Australian workshops — are among the most widely used fasteners in industrial and trade settings, and among the least understood. They are everywhere: locking pulleys to shafts, securing shaft collars to positioning rods, holding door levers to spindles, fixing mirror brackets to wall studs. Despite this, most tradespeople and engineers select them by habit rather than specification, grabbing whatever is in the parts bin rather than matching the point type, material, and thread form to the job. That habit works until it doesn't. A cup point socket set screw in a rotating shaft application will eventually fret and loosen under cyclic load where a dog point would have held. A standard alloy steel grub screw in a stainless shaft assembly will corrode and seize. A metric socket set screw in a BSW-tapped hole will cross-thread and strip. These failures are preventable with a basic understanding of how socket set screws work and how to select them correctly. This guide covers the complete picture: what socket set screws are and how they work, the point type options and when to use each, drive styles, materials, metric and imperial thread systems, sizing, installation, and how to deal with the most common failure mode — the stripped socket. This guide is part of AIMS Industrial's curated Engineering Reference Charts library — 78 reference articles across fasteners, threading, bearings, lubrication and safety standards. Socket Set Screw, Grub Screw, Set Screw — What's the Difference? These three terms all refer to the same fastener type, but they come from different contexts and carry slightly different meanings depending on where you are. "Socket set screw" is the precise technical product name used in Australian industrial supply. It tells you two things: the fastener is a set screw (fully threaded, headless, used to secure one component against another without a nut), and it is driven by a socket — specifically, a hex (Allen) socket, Torx socket, or square socket in the head. This is the term you will find on AIMS product labels, engineering drawings, and standards documents. "Grub screw" is the colloquial Australian and British term for the same fastener. It is what tradespeople, maintenance fitters, and most workshops call them. The term has no agreed etymology, but its use is consistent throughout Australia and the UK. If you ask a fitter for a grub screw, they will hand you a socket set screw. The two terms are interchangeable in practice. "Set screw" is the American term. In US engineering and industrial supply, a set screw (or "setscrew") is exactly what Australians call a grub screw or socket set screw. In some older British and Australian usage, "set screw" could refer to a headed screw used as a locking fastener, which creates occasional confusion — but in modern Australian industrial supply, "set screw" and "socket set screw" are used interchangeably. In this guide: "socket set screw" is used as the technical term; "grub screw" is used as the shorthand where appropriate. Both are correct in an Australian context. How Socket Set Screws Work A socket set screw is fully threaded from tip to top, with no head projecting above the surface it is threaded into. It engages a pre-tapped hole in one component — the collar, hub, or housing — and bears down on a second component — the shaft, surface, or flat — through the action of its tip (point). The threaded engagement holds the screw in place; the point transmits the clamping or locking force to the shaft or surface below. The mechanism is friction and compression. As the socket set screw is tightened, the point presses into or against the shaft surface. The threads pull the screw upward while the point presses down, creating a clamping force that locks the collar or hub to the shaft. This is not a shear connection — the screw is not taking the load in shear like a bolt through a flange. It is a friction/indentation lock. The holding force comes from the interface between the point and the shaft, not from the screw body. The implications of this are important: A socket set screw with a worn or rounded point has significantly reduced holding force, even if it appears fully tightened The point type determines whether the connection indents the shaft surface (cup, cone), sits flat on it (flat point), or engages a machined feature (dog point into a flat or hole) Vibration and cyclic loading work against the friction lock — thread locking compound is often needed for grub screws in dynamic applications An over-tightened cup point will permanently indent the shaft; this is sometimes intentional (positive location) and sometimes a problem (damaged shaft, difficulty repositioning) Because socket set screws are driven by a hex key inserted into the socket in the top of the screw (which sits flush with or below the component surface), they provide a clean, unobtrusive fastening — no protruding head to snag or interfere with adjacent components or guards. This is why they are used where space is constrained and where a flush finish is required. Point Types: The Most Important Selection Decision The point type is the most consequential choice when specifying a socket set screw. It determines how the screw engages the shaft or surface, what holding force it develops, whether it damages the shaft surface, and whether it can be repositioned after tightening. Most engineers and tradespeople default to cup point without considering the alternatives — this is often the right choice, but not always. Cup Point Cup point is the most common socket set screw point type. The tip has a shallow, circular cupped cavity surrounded by a sharp annular rim. When tightened against a shaft or surface, the rim bites into the material, creating a circular indentation that provides positive mechanical location in addition to friction. The cup point delivers high holding force for its size and resists axial and rotational movement under load. The trade-off is shaft marking. A fully tightened cup point will leave a visible and palpable ring indent in the shaft. On a hardened shaft this indent is slight; on a soft shaft it can be pronounced. This is generally acceptable in fixed-position applications — where the hub or collar is set once and not repositioned. Where repositioning along the shaft is likely, cup point causes progressive surface damage that can affect shaft seating accuracy over time. Use cup point for: Fixed shaft/hub locking where shaft marking is acceptable, shaft collars in set positions, sprocket and gear hub retention, general industrial applications where repositioning is unlikely. This is the go-to choice for the majority of socket set screw applications. Flat Point (Plain Point) Flat point socket set screws have a flat, ground tip — no raised rim, no indent geometry. The flat end bears against the shaft surface over a broader contact area than cup point, which distributes the load rather than concentrating it at the rim. The flat point does not significantly indent soft shaft materials, which makes it preferable where shaft surface integrity matters or where the screw must not damage a polished or plated surface. The holding force of a flat point is lower than cup point at the same torque because there is no mechanical interlock from shaft indentation. The connection is purely frictional. Flat points are also used on the end of adjustment screws and pressure pads where the flat face needs to transmit thrust without rotation or side load. Use flat point for: Locking against finished or plated surfaces where marking is unacceptable, adjustment screws bearing against hardened pads, applications where the component must be repositioned without shaft damage, and as a thrust/pressure point on adjustment assemblies. Oval Point Oval point has a convex, rounded dome tip — partway between flat point and cone point. The rounded tip makes light contact with the shaft surface across a small area, produces minimal shaft marking, and seats well on curved or uneven surfaces. It is forgiving of slight angular misalignment between the screw axis and the shaft. Oval point is less common in standard industrial catalogues than cup or flat, but is useful in fine adjustment applications where a low-friction, low-marking point is needed and where the screw will be adjusted frequently. The rounded tip slides more easily over the shaft surface during adjustment than a flat or cup point would. Use oval point for: Fine adjustment screws requiring frequent repositioning, applications with curved contact surfaces, and where minimal shaft marking combined with reasonable friction retention is needed. Cone Point Cone point has a sharp conical tip designed to be used with a matching conical indent (centre punch mark or drilled dimple) on the shaft. The cone seats into the indent, providing positive location that resists both axial and rotational displacement. Once seated, a cone point grub screw provides higher resistance to rotation than cup point because the engagement is a three-dimensional taper fit rather than a flat rim bite. The limitation is that the cone point is only fully effective with a matching indent on the shaft. Without the indent, the cone point contacts the shaft on its tip only, which concentrates load on a very small area and can gouge or scratch hardened shafts. Cone point is also permanent in the sense that the shaft dimple becomes the location reference — repositioning to a new location requires a new dimple. Use cone point for: Permanent or semi-permanent locking into a pre-punched or drilled dimple on the shaft, applications requiring maximum resistance to both axial and rotational displacement, and where the location point on the shaft needs to be defined precisely. Common in precision instruments and spindle applications. Dog Point Dog point has a cylindrical pilot projection extending from the tip, smaller in diameter than the screw body. This pilot engages a mating hole or flat ground on the shaft, providing a positive mechanical connection that is significantly stronger in shear than a friction-only cup or flat point connection. The dog point effectively acts as a key — the pilot enters a cross-drilled hole or an axial flat on the shaft and physically prevents rotation of the hub or collar relative to the shaft. Dog point socket set screws are the correct choice for rotating applications under significant torque — gear hubs, sprocket drives, coupling flanges — where a cup point friction connection would loosen under cyclic load. The pilot diameter is standardised to match common shaft flat dimensions. Dog points require more preparation than other point types (a cross-hole or flat must be machined on the shaft) but provide a mechanically superior connection for demanding applications. Use dog point for: Rotating shaft/hub connections under torque load, coupling and drive applications where a friction connection is insufficient, applications where the hub must be locked positively against rotation and axial movement, and as a positive locating pin where the point engages a transverse hole. Half Dog Point Half dog point (also called half cone or stub dog) is a shortened dog point pilot — approximately half the standard dog point length. It is used where the shaft depth available for the pilot engagement is limited, or where a less aggressive mechanical interlock is acceptable. The shorter pilot provides positive location but less resistance to axial pull-out than a full dog point. Use half dog point for: Applications with limited shaft engagement depth, where full dog point is specified but space dictates a shorter pilot, and as a cross-pin engagement screw in thinner-walled applications. Knurled Cup Point Knurled cup point has a cup-shaped tip with a knurled or serrated rim rather than a smooth rim. The serrations bite more aggressively into the shaft surface than a plain cup point, providing higher resistance to rotation under dynamic load. This increases holding force at the cost of more pronounced shaft surface marking. Knurled cup is often specified in high-vibration environments where cup point retention has been found inadequate, and where the additional shaft indentation from the serrated rim is acceptable. AIMS stocks Soko M12 knurled cup point socket set screws in this configuration. Use knurled cup point for: High-vibration applications requiring higher rotational resistance than plain cup, heavy rotating drive components, and applications where dynamic loads have caused plain cup points to loosen. Point Type Summary Table Point Type Shaft Marking Holding Force Repositionable? Best For Cup Moderate (ring indent) High Limited General fixed-position shaft locking Flat Minimal Moderate Yes Finished surfaces, adjustment screws Oval Very low Moderate Yes Frequent adjustment, curved surfaces Cone High (requires dimple) Very high No Permanent precision location Dog None (engages hole/flat) Highest No (requires prep) Torque-loaded rotating shafts Half Dog None High No (requires prep) Limited depth dog point engagement Knurled Cup High (serrated indent) Very high No High-vibration rotating applications Drive Styles The drive style refers to the socket type in the top of the screw — the recess that accepts the Allen key or other drive tool. For socket set screws, the dominant drive style is hexagonal socket (Allen socket), which is why "hex key" and "grub screw" are so closely associated. Hex Socket (Allen Drive) Hexagonal socket is the standard drive for Australian socket set screws. A hex key (Allen key) is inserted into the socket and rotated to tighten or loosen the screw. The hex socket drive is compact, allows the screw to sit fully recessed below the component surface, and transmits high torque for its small footprint. The socket size is directly related to the screw diameter — see the sizing section for the hex key size per thread size. For more on hex key types, sizes, and selection — including ball-end keys, T-handles, and the metric/imperial size chart — see our Allen Key & Hex Key Guide. Torx Socket Torx (star) drive socket set screws are available in some size ranges. Torx provides better torque transmission than hex socket at small sizes because the star geometry distributes load across six lobes rather than six flats, and is less prone to cam-out under high torque. Torx socket grub screws are more common in precision instrument and electronics applications where small screw sizes (M2–M4) are used and driver engagement is critical. Slotted Head Some older-pattern socket set screws use a straight slot rather than a socket drive, engaged by a flat-blade screwdriver. Slotted grub screws are largely obsolete in industrial applications — the torque that can be transmitted is low, cam-out risk is high, and the slot offers no advantage over hex socket. They appear in older British-standard applications and in some domestic hardware (furniture fittings, mirror fixings). Do not confuse with standard grub screws when ordering replacements. Square Socket (Bristol/Bristo Drive) Square socket or Bristol-pattern drive is found in some older American and British-standard socket set screws, particularly in larger imperial sizes. The square socket transmits high torque and was widely used before hex socket became dominant. Still encountered in legacy plant and equipment. If you find a grub screw with a square recess that your Allen keys won't fit, it is almost certainly a square-drive (Bristol) socket — Bristol key sets are available. Materials and Grades The material and grade of a socket set screw determines its hardness, strength, corrosion resistance, and suitability for the application environment. Selecting the wrong material is one of the most common and consequential errors in socket set screw specification. High Grade Alloy Steel High grade alloy steel is the standard material for industrial socket set screws. This covers the ISO property class 45H designation — a medium carbon alloy steel heat-treated to provide hardness suitable for grub screw applications. Class 45H socket set screws are significantly harder than standard grade 8.8 cap screws, which is necessary because the cup or cone point must be harder than the shaft material it is indenting. A soft point will deform on contact with a hardened shaft and lose its holding function. High grade alloy steel socket set screws are typically supplied with a black oxide or plain (bright) finish. Black oxide provides minimal corrosion resistance (suitable for dry indoor applications with periodic lubrication) and is primarily a cosmetic and anti-galling treatment. Plain finish provides no corrosion protection. Neither is suitable for outdoor, marine, or chemical environments without additional protection. Stainless Steel (304 and 316) Stainless socket set screws are specified for applications requiring corrosion resistance — food processing equipment, marine and coastal environments, chemical plant, outdoor installations, and any environment where steel would corrode unacceptably. AIMS stocks both 304 and 316 stainless socket set screws. The material grade matters: 304 stainless (A2): The general-purpose stainless option. Good corrosion resistance in most atmospheric and mildly aggressive environments. Not suitable for chloride-rich environments (coastal, marine, salt spray, chlorinated water systems) — 304 is susceptible to chloride pitting. 316 stainless (A4): Contains molybdenum, which significantly improves chloride resistance. The correct choice for marine, coastal, food processing (where CIP cleaning with chlorinated solutions is used), and chemical plant applications. Meaningfully more expensive than 304 but specified correctly in these environments. Critical note on stainless strength: Austenitic stainless steel (304 and 316) in the annealed condition has lower yield strength than alloy steel socket set screws — approximately equivalent to a grade 4.6 or 5.8 bolt, not a class 45H set screw. Stainless socket set screws are softer than their alloy steel equivalents and should not be used against hardened shafts where the point is expected to indent the shaft material. The stainless point will deform before it indents a hardened shaft. Galling risk: Stainless fasteners are susceptible to galling (cold welding) when threaded into stainless tapped holes. Stainless-on-stainless threading can seize with only moderate torque, permanently fusing the screw in place. If you are fitting a stainless socket set screw into a stainless tapped hole (stainless shaft collars, stainless housings), apply an anti-seize compound designed for stainless before installation. This is not optional in stainless-on-stainless applications. Brass Brass socket set screws are used in applications requiring non-magnetic, non-sparking, or electrically conductive properties — electrical equipment, instrumentation, explosive atmosphere environments, and applications where the screw must not damage soft shafts (brass is softer than most shaft materials, so it will deform before indenting the shaft). Brass is also used in decorative applications where the visible end of the screw needs to blend with brass fittings. Brass has good corrosion resistance in atmospheric and freshwater environments but should not be used in contact with ammonia solutions or certain acids. Nylon-Tipped Nylon-tipped socket set screws have a standard alloy steel body with a nylon or plastic insert at the point. The nylon tip bears against the shaft instead of the steel point, providing a non-marring, electrically insulating interface. They are used in precision instruments and optical equipment where shaft marking is unacceptable, in electrical applications where the screw must not create a conductive path, and in applications where the shaft material is too soft to accept a metal point without damage. The nylon insert is replaceable in some configurations. The holding force is lower than a metal point because the nylon deforms under load rather than interlocking with the shaft surface. Not suitable for high-torque or vibration-heavy applications. Thread Systems: Metric and Imperial Socket set screws in Australia are supplied in metric and three imperial thread systems. The correct thread system must match the tapped hole in the component you are assembling — thread systems are not interchangeable, and using a metric screw in an imperial hole (or vice versa) will cross-thread and damage both the screw and the tapped hole. Metric Metric is the default thread system for new plant, machinery, and fabrication in Australia. Metric socket set screws follow the ISO/DIN standard coarse thread pitch for each diameter. The standard range runs from M2 to M20, with M3 through M12 the most commonly stocked sizes in industrial supply. Standard coarse pitch is almost always correct for socket set screw applications — fine pitch metric grub screws exist but are uncommon and usually only specified in precision instrument applications. BSW — British Standard Whitworth BSW (British Standard Whitworth) is the old British imperial thread form that was standard in Australian manufacturing and plant from colonial settlement through to metrication in the 1970s. BSW uses a 55° thread form (distinct from the 60° thread form of metric and UNC/UNF) with thread pitches specified in threads per inch. BSW socket set screws are still actively stocked and used in Australia because a large installed base of older British-origin plant, mining equipment, agricultural machinery, and marine equipment remains in service. If you are servicing pre-metrication machinery — particularly British-manufactured equipment from before approximately 1975 — you are likely to encounter BSW threads. Standard sizes in AU industrial supply run from ¼" to 1". BSW threads are not interchangeable with UNC or UNF threads of the same nominal diameter. A ½" BSW bolt will not fit a ½" UNC nut. The thread pitch and form are different. UNC — Unified National Coarse UNC is the American imperial coarse thread standard, using a 60° thread form with threads per inch pitch specified for each diameter. UNC is the dominant imperial thread in American-specification machinery, equipment, and tooling, and is widely used in Australian industries with American equipment: mining, resources, oil and gas, agriculture (John Deere, Case IH, etc.), and imported American-brand industrial plant. UNC socket set screws are the correct replacement when servicing American-spec equipment with imperial threads. Standard Australian industrial supply covers sizes from approximately ¼" to 1½". UNF — Unified National Fine UNF is the American imperial fine thread standard — more threads per inch than UNC at the same nominal diameter. The finer thread pitch provides higher thread engagement force per turn and better resistance to vibration loosening, at the cost of more turns to assemble and greater sensitivity to thread damage on installation. UNF socket set screws are used in precision assemblies and where the standard UNC thread is specified as "fine" in the original equipment documentation. Less commonly stocked than UNC but available in the standard size range. AIMS stocks UNF in sizes including 7/16" and ½". Quick Identification: Which Thread Do I Have? If you need to identify an existing socket set screw's thread, the practical approach is: Measure the outer (major) diameter with verniers. Metric sizes will be close to a whole millimetre (M6 = 6.0mm, M8 = 8.0mm). Imperial nominal sizes will be close to a fractional inch (½" = 12.7mm, 3/8" = 9.5mm). If imperial, use a thread gauge or pitch gauge to count threads per inch. Compare against BSW, UNC, and UNF pitch charts for the relevant diameter — the pitch differs enough between systems to be distinguishable with a thread gauge. When in doubt on older AU plant: check the machinery plate or manufacturer's specification. Pre-1975 British equipment is almost certainly BSW; post-1975 American equipment is almost certainly UNC/UNF; post-1975 Australian/European equipment is almost certainly metric. Metric Sizing: Dimensions and Allen Key Reference Metric socket set screws are specified by thread diameter (M-size) and length. Length is measured as the full screw body length from tip to top — because there is no head, the screw is entirely within the tapped hole when installed, and the length is simply the thread engagement depth. Thread Size Hex Key Size (AF) Common Lengths (mm) Typical Applications M2 0.9mm 2, 3, 4, 5 Precision instruments, small mechanisms M2.5 1.3mm 3, 4, 5, 6 Instruments, electronics M3 1.5mm 3, 4, 5, 6, 8, 10 Small shaft collars, light duty M4 2mm 4, 5, 6, 8, 10, 12 Shaft collars, light mechanical M5 2.5mm 5, 6, 8, 10, 12, 16 General mechanical, small pulley hubs M6 3mm 6, 8, 10, 12, 16, 20 Common industrial — shaft collars, couplings M8 4mm 8, 10, 12, 16, 20, 25 Medium industrial — drive hubs, sprockets M10 5mm 10, 12, 16, 20, 25, 30 Medium-heavy drive components M12 6mm 12, 16, 20, 25, 30, 35 Heavy industrial shafts and hubs M16 8mm 16, 20, 25, 30, 35, 40 Large shaft locking M20 10mm 20, 25, 30, 35, 40 Heavy machinery shafts The hex key size relationship: For metric socket set screws, the hex socket size (across-flats, AF) is approximately half the thread diameter — M6 takes a 3mm key, M8 takes a 4mm key, M10 takes a 5mm key. This is a useful rule of thumb but not universally precise at small sizes (M2, M2.5, M3). When in doubt, use the table above or check the manufacturer's specification. For the full hex key size reference across metric and imperial, including ball-end key dimensions and long-arm key sizes, see our Allen Key & Hex Key Guide. Imperial Sizing Reference Thread System Nominal Diameter Hex Key Size Common Context in AU 3/16" BSW / UNC 4.76mm 3/32" Light British/American equipment 1/4" BSW / UNC / UNF 6.35mm 1/8" Common — legacy AU plant, American equipment 5/16" BSW / UNC / UNF 7.94mm 5/32" Common — drives, shaft collars 3/8" BSW / UNC / UNF 9.53mm 3/16" Common — medium shafts 7/16" BSW / UNC / UNF 11.11mm 7/32" Medium — American equipment 1/2" BSW / UNC / UNF 12.70mm 1/4" Common heavy — conveyors, drives 5/8" BSW / UNC 15.88mm 5/16" Heavy machinery 3/4" BSW / UNC 19.05mm 3/8" Large shaft locking 1" BSW / UNC 25.4mm 1/2" Heavy plant 1-1/2" UNC 38.1mm 3/4" Heavy American-spec plant Note on BSW vs UNC at the same nominal size: BSW and UNC share the same nominal diameter (both use fractional inch designations) but have different thread pitches and thread forms. A ½" BSW has 12 TPI; a ½" UNC has 13 TPI. A ½" UNF has 20 TPI. They will not interchange. Always verify the thread system before ordering replacements. Applications Shaft and Hub Locking The most common industrial application for socket set screws is locking a hub, collar, or sleeve to a shaft — preventing both axial movement (along the shaft) and rotational movement (around the shaft). This covers: sprocket and timing pulley hubs, coupling halves, shaft collars used as mechanical stops, encoder and sensor mounting collars, impeller hubs on pumps, and fan hub assemblies. For static applications with light to moderate load, a cup point socket set screw provides adequate holding force. For rotating applications under significant torque — drive sprockets, coupling flanges, high-speed pulleys — dog point into a machined flat or cross hole provides a mechanically stronger connection. Two socket set screws offset 90° or 120° around the collar circumference distribute the load and reduce the risk of the collar walking around the shaft. Shaft Collars Shaft collars are a specific and important application. There are two collar types: set-screw collars (one or two socket set screws through the collar bore clamping against the shaft) and clamp collars (the collar is split and compressed around the shaft by cap screws tightening the split gap). Set-screw collars are simpler and less expensive; clamp collars distribute load more evenly around the shaft circumference and are preferred for precision positioning and for shafts where surface damage is unacceptable. For set-screw shaft collars, cup point is standard. Dog point into a machined flat is used where higher axial and rotational resistance is required. The shaft collar is a common context where the socket set screw is doing the entire job of locating and locking the collar — the screw selection directly determines whether the collar stays put under load. Door Hardware and Domestic Fittings Door lever handles, knobs, and pull handles are almost universally locked to their spindles with one or two socket set screws — the small hex socket screw you find on the underside or back of the handle rose or on the handle shank. These are typically metric M4 or M5 in residential hardware, and M6 in commercial hardware. When a door lever loosens or spins on its spindle, a stripped or loose grub screw is the first thing to check. Bathroom and kitchen tapware uses socket set screws to lock handles to valve spindles. Stainless steel grub screws are often specified here to prevent corrosion in wet environments. Mirror and Shelf Bracket Fixings Frameless mirror mounting systems, shelf bracket systems, and some rail mounting hardware use socket set screws to clamp components to mounting rods or rails. These are typically small metric sizes (M4–M6) with flat or cup point, where the screw must hold the component in a set position on the rod without damaging the rod surface excessively. Electronics and Instrument Enclosures Panel mount connectors, BNC and SMA RF connectors, instrument shaft encoders, and potentiometers often use very small socket set screws (M2–M3) to lock components to shafts or to secure covers. Torx or hex socket drive at these small sizes. Nylon-tipped or brass point types are common where shaft damage must be avoided and where electrical isolation between the screw and the shaft is required. Installation: Getting It Right Check Thread System and Size First Before installing any socket set screw, confirm the thread system (metric, BSW, UNC, or UNF) and the nominal diameter match the tapped hole. If a screw starts easily by hand for the first two or three turns and then suddenly becomes stiff, stop — this is the symptom of a thread mismatch. Forcing a mismatched screw will cross-thread and damage the tapped hole. The correct fit is smooth hand threading for the full depth. Hex Key Quality and Size Using a worn, undersized, or wrong-system hex key is the single most common cause of stripped sockets. A metric 3mm key in a 3mm metric socket sets correctly; an imperial 1/8" key (3.175mm) is slightly too large and will not seat fully, creating corner contact that rounds out the socket when torque is applied. Always verify metric vs imperial before applying force. Quality hex keys with hardened tips and accurate dimensions make a significant difference to socket longevity, particularly at small sizes (M3–M6) where the socket wall is thin. A chrome vanadium or S2 steel hex key will transmit full torque without deforming; a cheap key will round its own corners before rounding the socket. Ball-end hex keys are convenient for reaching at angles but should only be used to start and run down the screw — apply final tightening torque with the straight end fully seated, not the ball end, which contacts the socket at an angle and transfers torque less efficiently. See our Allen Key & Hex Key Guide for a full breakdown of key types, sizes, and selection for different applications. Tightening Torque Socket set screws should be tightened to the torque value specified for the thread size and grade. Over-tightening a cup point in a soft shaft will indent the shaft excessively; over-tightening in a hard shaft can shear the screw. Under-tightening will allow the connection to loosen under vibration or load. Indicative tightening torques for class 45H alloy steel socket set screws: Thread Size Torque (Nm) M3 0.5–0.8 M4 1.2–1.5 M5 2.0–2.5 M6 3.5–4.5 M8 9–12 M10 18–22 M12 30–38 These are indicative figures for alloy steel screws. Stainless socket set screws should be tightened to lower values (approximately 70–80% of the alloy steel torque) to reduce the risk of galling. Thread Locking Compound Socket set screws in vibrating machinery should be secured with a thread locking compound to prevent loosening. Loctite 243 (medium strength, blue) is the standard choice for most socket set screw applications — it allows disassembly with hand tools when needed. Apply a single drop of thread locker to the thread before installation and tighten immediately; do not allow to cure before tightening. Full cure strength is reached after approximately 24 hours at room temperature. Loctite 271 (high strength, red) is used where the set screw must never loosen — precision position-critical applications — but requires heat (approximately 230°C) for disassembly. Use 243 unless permanent lock is specifically required. Do not use thread locking compound on stainless-on-stainless assemblies without also applying anti-seize — the combination of galling risk and thread locker can make a stainless set screw effectively permanent without heat. Removing a Tight or Stripped Socket Set Screw The stripped socket is the most common grub screw problem encountered in practice. Once a socket rounds out, the hex key turns without engaging the socket walls and the screw cannot be turned. This happens most often from: using a worn or incorrect key, applying torque at an angle with a ball-end key, using a metric key in an imperial socket or vice versa, or simply applying too much force on a small socket. Step 1 — Check the other system first. If a metric key rounds out at a given size, try the next imperial size (or vice versa). A moderately stripped M5 socket may respond to a 5/32" imperial key (3.97mm) which is slightly smaller than the worn metric socket opening and can bite on remaining material. This is the simplest fix and works more often than expected. Step 2 — Apply penetrating oil and heat. If the screw is seized in addition to being stripped, apply penetrating oil (CRC, WD-40 Specialist Penetrant) to the thread area and allow to soak. For steel screws in steel or aluminium, a brief application of heat from a soldering iron or heat gun to the surrounding material will cause thermal expansion that can break the thread seizure. Do not use an open flame near thread locking compounds or lubricants. Step 3 — Use a diamond-tipped or knurled hex key. Some manufacturers produce hex keys with a diamond-coated or knurled working surface specifically for extracting rounded sockets. The abrasive surface bites into partially rounded socket walls and can transmit enough torque to turn the screw. Try this before drilling. Step 4 — Torx key in a stripped hex socket. Selecting a Torx key one size up from the socket dimensions and tapping it lightly into the stripped hex socket with a small hammer can create enough engagement to turn the screw. The Torx star geometry bites into the remaining socket material. Step 5 — Screw extractor. Left-hand spiral extractors (EZ-Out type) can be driven into the stripped socket with a centre punch or small hammer and then turned anticlockwise with a tap wrench or socket. As the extractor bites the socket walls and is turned, it simultaneously loosens the screw. This works well on screws that are not fully seized. Step 6 — Drill out. If all else fails, the screw body must be drilled out, leaving the thread in the housing intact. Use a drill bit slightly smaller than the screw's minor (root) diameter to remove the screw body without damaging the thread. After removing the body, the remaining thread can often be wound out with a dental pick or sharp probe. This is the most reliable method of last resort but requires patience and accurate drilling to avoid destroying the tapped hole. Socket Set Screw Selection Guide Application Recommended Point Material Thread System Notes Fixed shaft collar, general use Cup point Alloy steel Metric (new plant) Standard choice for most applications Rotating drive hub under torque Dog point Alloy steel Metric / UNC Machine flat or cross-hole on shaft required High-vibration rotating application Knurled cup Alloy steel Metric Use thread locker (Loctite 243) Precision instrument location Cone point Alloy steel or brass Metric Pre-punch or drill dimple on shaft Finished surface, no shaft marking Flat point Brass or alloy steel Metric Lower holding force — verify adequacy Soft shaft, no marking allowed Nylon-tipped Alloy steel (nylon tip) Metric Reduced holding force Door hardware / domestic fitting Cup point Zinc plated steel or SS Metric (M4–M6) Replace with stainless in wet areas Food processing / wash-down Cup or flat 316 stainless Metric Anti-seize on SS-on-SS assembly Marine / coastal environment Cup or flat 316 stainless Metric or BSW 316 not 304 in chloride environments Legacy British plant (pre-1975 AU) Cup point Alloy steel BSW Verify with thread gauge before ordering American-spec machinery Cup point Alloy steel UNC or UNF UNF for fine-thread specification Explosive / non-sparking environment Cup or flat Brass Metric Verify Ex classification requirements Frequently Asked Questions What is a socket set screw? A socket set screw — commonly called a grub screw in Australia — is a fully threaded, headless fastener used to secure one component against another without a nut. It threads into a tapped hole in one component (a collar, hub, or housing) and presses its point against a second component (typically a shaft or surface), locking the two together through friction and point engagement. Because there is no projecting head, the screw sits fully flush with or below the surface of the component it is threaded into. The "socket" in the name refers to the hex, Torx, or square recess in the top face that accepts the drive key. What is the difference between a grub screw and a socket set screw? Nothing — they are the same fastener. "Socket set screw" is the precise technical product name used in Australian industrial supply. "Grub screw" is the colloquial Australian and British term for the same thing. Both terms are in common use in Australian workshops and on engineering drawings. The American equivalent term is "set screw." What is the most common grub screw point type? Cup point is the most common point type for general industrial socket set screw applications. The cup point has a sharp annular rim that bites into the shaft surface on tightening, creating both a friction lock and a mechanical indentation that resists axial and rotational movement. It provides a good balance of holding force, ease of installation, and availability across all sizes and thread systems. Dog point is specified when a cup point friction connection is insufficient — typically in rotating drive applications under significant torque. What size Allen key do I need for a grub screw? For metric socket set screws, the hex key size is approximately half the thread diameter — an M6 takes a 3mm key, an M8 takes a 4mm key, an M10 takes a 5mm key, an M12 takes a 6mm key. This ratio is a reliable guide for M4 and larger. At smaller sizes (M2, M2.5, M3), check the table rather than assuming the half-diameter rule. For imperial socket set screws, the hex key size is specified in fractional inches — a ½" BSW or UNC set screw typically takes a ¼" hex key. Always verify metric vs imperial before applying torque — using a metric key in an imperial socket (or vice versa) is the most common cause of stripped sockets. For full hex key sizing across all systems, see our Allen Key & Hex Key Guide. What is the difference between BSW, UNC, and metric socket set screws? These are three different thread systems that are not interchangeable. Metric uses the ISO thread form (60° thread angle, pitch in mm). BSW (British Standard Whitworth) uses a 55° thread form with pitch in threads per inch — found in older British and Australian-heritage plant and equipment. UNC (Unified National Coarse) uses a 60° thread form with pitch in threads per inch — the standard American imperial thread, used in American-specification machinery. Screws from one system will not thread correctly into a hole tapped for another system, even at the same nominal diameter. When replacing a socket set screw, always confirm the thread system before ordering. Should I use stainless steel socket set screws? Use stainless where corrosion resistance is required — food processing, marine, coastal, wash-down environments, and outdoor installations. Select 316 stainless for chloride-rich environments (coastal, salt spray, CIP cleaning with chlorinated solutions); 304 is adequate for general atmospheric and mild environments. Two important limitations: first, stainless socket set screws are softer than alloy steel equivalents and should not be used against hardened shafts where the point must indent the shaft material. Second, stainless-on-stainless thread assemblies are susceptible to galling (cold welding) — always apply anti-seize compound designed for stainless when threading a stainless set screw into a stainless tapped hole. When should I use a dog point instead of a cup point? Use a dog point when the connection must resist torque or axial load that exceeds what a cup point friction connection can reliably hold. The dog point has a cylindrical pilot that engages a machined flat or cross-hole on the shaft, providing a positive mechanical interlock rather than a friction-only connection. This is the correct specification for rotating drive hubs — sprockets, pulleys, coupling flanves — under significant transmitted torque, where a cup point set screw may loosen over time under cyclic load. Dog point requires a matching machined feature on the shaft (a flat or a drilled hole to suit the pilot diameter); it cannot be used on an unmodified round shaft. Can I use thread locker on socket set screws? Yes, and it is recommended in vibrating machinery applications. Loctite 243 (medium strength, blue) is the standard choice — it prevents vibration loosening and allows disassembly with hand tools when needed. Apply a single drop to the thread before installation. For permanent locking where the screw should never loosen, Loctite 271 (high strength, red) can be used, but requires heat for disassembly. For stainless-on-stainless assemblies, apply anti-seize first and then thread locker on top if vibration resistance is needed — do not rely on thread locker alone to prevent galling in stainless assemblies. Why does my grub screw keep coming loose? The most common causes of socket set screw loosening are: vibration in the assembly without thread locking compound; insufficient tightening torque on initial installation; a worn or rounded cup point that has lost its shaft indentation and provides only residual friction; and a cup point on a shaft that is too hard for the point to indent (giving only metal-to-metal contact without bite). The fix for vibration loosening is Loctite 243. The fix for a worn point is replacement. The fix for a hard shaft with no bite is to switch to a dog point with a machined engagement feature, or to use knurled cup point which bites more aggressively than plain cup. How do I remove a stripped socket set screw? Work through these options in order: (1) Try the other thread system's key — a slightly smaller imperial key in a stripped metric socket (or vice versa) can bite remaining socket material. (2) Apply penetrating oil and, if the screw is seized, heat the surrounding material with a soldering iron or heat gun to break thread seizure. (3) Use a diamond-tipped or knurled hex key designed for stripped socket extraction. (4) Drive a Torx key slightly larger than the socket into the rounded recess and turn anticlockwise — the Torx star geometry bites into remaining material. (5) Use a left-hand spiral screw extractor driven into the socket. (6) Drill out the screw body with a bit slightly smaller than the thread minor diameter, then pick out the remaining thread material. Taking the time to use the correct key at the correct size prevents stripped sockets — most stripping is caused by metric/imperial mix-up or worn keys. What grade are standard socket set screws? Standard alloy steel socket set screws are supplied to ISO property class 45H, which specifies a minimum Vickers hardness of 45 HRC. This is significantly harder than standard structural bolts (8.8 grade has approximately 24 HRC equivalent) because the point of the set screw must be hard enough to indent or bear against shaft materials without deforming. Stainless steel socket set screws are supplied to A2-70 (304 SS) or A4-70 (316 SS) — equivalent to approximately 23 HRC, which is considerably softer than class 45H alloy steel. Stainless set screws should not be used in applications where the point must penetrate a hardened shaft surface. What is a knurled cup point socket set screw? A knurled cup point socket set screw has a cup-shaped point with a serrated or knurled rim instead of a smooth rim. The serrations bite more aggressively into the shaft surface on tightening than a plain cup rim, increasing resistance to rotational displacement under dynamic load. This makes knurled cup point the preferred choice in high-vibration applications or where a plain cup point connection has been found to loosen under operating conditions. The trade-off is more pronounced shaft surface marking than plain cup point. Shop Socket Set Screws at AIMS Industrial AIMS Industrial stocks metric and imperial socket set screws across all major point types and materials — cup point, dog point, flat point, knurled cup — in alloy steel, 304 stainless, 316 stainless, and high-grade alloy steel. Thread systems stocked include Metric, BSW, UNC, and UNF. Shop Socket Set Screws Our Tap Types guide covers every cutting and forming tap variant with material-specific selection rules. People Also Ask — Grub Screws Q: What is the difference between a grub screw and a set screw? This guide explains: in Australian and British English, "grub screw" and "set screw" refer to the same fastener — a fully threaded, headless fastener driven by a hex key or screwdriver socket. In American English, "set screw" is the standard term. Both terms appear on Australian packaging and in search results. AIMS and most Australian suppliers use "grub screw" as the primary term. Q: What are the different point types for grub screws? This guide covers the full range: cup point is the most common — the circular rim grips the mating surface. Cone point bites into the surface for a more permanent hold. Flat point is used where surface marking must be minimised. Dog point adds a plain cylindrical stub for positive location against a flat on a shaft. Oval point provides a softer contact for use on hard or precision shaft surfaces. Q: How does a grub screw work? As this guide explains, a grub screw is threaded into a tapped hole in a hub, collar, or boss so that its point contacts the shaft or mating surface beneath. When tightened, the point applies direct pressure to the shaft — either gripping it frictionally (cup or flat point) or biting into it for a more positive mechanical lock (cone or dog point). This transmits torque or holds axial position without requiring a key or retaining ring. Q: What materials are grub screws available in? Covered in this guide: alloy steel with black oxide finish is standard for most industrial applications. Stainless steel Grade 316 or 304 suits corrosive environments, marine use, and food-adjacent applications. Brass grub screws are used where marking soft shafts must be avoided or where electrical conductivity is needed. Material choice affects corrosion resistance, point hardness, and maximum permissible torque. Q: What drive style should I use for grub screws? This guide details the options: hex socket (Allen key) drive is standard for industrial grub screws — accessible in assembled components, resistant to cam-out, and available in a wide size range. Slotted drive appears in older or lower-precision applications. Hex socket is the default for engineering and maintenance work, and the hex key size is standardised to thread diameter, so key selection is straightforward. Need screw pitch gauges? Browse the AIMS range at screw pitch gauges.
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Walk into any industrial supplier and you'll find a wall of work gloves. Leather. Nitrile. Cut-resistant. Chemical. Anti-vibration. Welding..
Read moreTypes of Pliers Guide: Types, Sizes & Selection
There are more than a dozen distinct plier types in regular use in Australian trade and industrial environments, and several of them share enough visual similarity that they get grabbed interchangeably — which is where the damage happens. Multigrip pliers used where combination pliers belong. Side cutters confused with flush cutters. Locking pliers forced onto a fastener that needs a proper wrench. Each substitution costs time or causes damage, and most of it is avoidable with a clear picture of what each tool is actually designed to do. This guide covers the 13 plier types most relevant to Australian trade and industrial practice — what each is designed for, how it works, what it's called in AU versus US and UK contexts, and how to select the right one for the job. Jewellery and hobby pliers are outside scope — this guide is written for the maintenance fitter, sparky, mechanic, or tradie who needs tools that work under load, every day. What are pliers? Pliers are hand tools that use a pivot — a rivet or pin at the junction of the two arms — to multiply the force applied to the handles and transfer it to the jaws. Squeezing the handles together closes the jaws; the leverage ratio of handle length to jaw length determines how much grip force is generated from hand pressure. The key components of any pair of pliers are: Jaws — the working surfaces. May be flat, serrated, round, tapered, angled, or profiled for specific tasks. Jaw geometry determines what the plier can grip or cut. Cutting edges — present on combination, side-cutting, and linesman pliers. Positioned at the pivot or at the jaw tip depending on type. Pivot — the joint. Fixed in most pliers (combination, long nose, side cutters); adjustable in multigrips, slip joints, and channel-lock types. Handles — bare steel on most trade pliers. Insulated handles (VDE 1,000V rated) on electrical pliers — required for live electrical work in Australia. Pliers fall into two broad functional families. Gripping pliers hold, bend, or turn material — combination, long nose, multigrip, locking, slip joint, and plier wrench types. Cutting pliers sever wire, cable, or rod — side cutters, diagonal cutters, linesman pliers, and flush cutters. Many types combine both functions in a single tool. Combination pliers Combination pliers — called "combination pliers" in Australia and the UK, and sometimes "engineer's pliers" — are the standard general-purpose plier for electrical work, maintenance, and light mechanical tasks. They combine three functions in one tool: serrated flat jaws for gripping, a curved jaw section for round stock and cable, and a side cutting edge set near the pivot for cutting wire. The name "combination" refers to these combined functions, not to adjustability. The pivot is fixed — combination pliers have one jaw opening size, which is their limitation compared to multigrip pliers for large or irregular work. Common sizes are 160mm, 180mm, and 200mm. The 180mm is the standard for most electrical and maintenance applications. VDE-rated insulated combination pliers (tested to 1,000V AC) are the required tool for work on live electrical systems under Australian electrical safety legislation — the insulation is a safety requirement, not an optional extra. ℹ AU vs US terminology: In Australian and UK usage, "combination pliers" describes this general-purpose gripping/cutting tool. In US usage, "combination pliers" sometimes refers to the same tool, but US electricians more often use the term "lineman's pliers" for a heavier electrician's tool that is a distinct product (covered separately below). Do not assume a US specification for "combination pliers" matches the AU/UK product. Long nose pliers (needle nose pliers) Long nose pliers — also called needle nose pliers — have elongated, tapered jaws that come to a point. Both terms are used in Australia; "long nose" is marginally more common in trade catalogues, while "needle nose" is widely understood. They are the same tool. The narrow jaw profile allows access to confined spaces where standard combination pliers cannot reach: inside electrical enclosures, behind panels, in engine bays, and in electronics assembly. The serrated gripping surfaces hold wire and small components; most long nose pliers also include a side cutter set near the pivot for wire cutting. Key variants: Standard long nose — straight taper. The most common form; 150mm and 180mm are the typical trade sizes. Bent nose pliers — the jaw is angled at 45° or 90° near the tip. Used when the access angle prevents a straight jaw from reaching the workpiece. Common in electrical panel work and plumbing behind fittings. Round nose pliers — cylindrical jaw tips with no serrations. Used for forming wire loops and coils — not primarily a gripping tool for trade applications. VDE insulated long nose — 1,000V rated. Required for live electrical work on wiring and terminal connections in confined spaces. Long nose pliers are precision tools, not force tools. Do not use them to grip large fasteners or apply torsional force — the tapered jaw geometry concentrates stress at the tip, and the tips bend or crack under load not suited to the design. Multigrip pliers Multigrip pliers are adjustable gripping pliers with a sliding or ratcheting pivot that allows the jaw opening to be set across a wide range — typically covering pipe, fittings, nuts, and irregular shapes from small to 50mm+ depending on model. They are the most versatile heavy gripping plier in a tradesperson's kit. ℹ What are they called? This single plier type has more names than any other: multigrips or multi grip pliers (dominant Australian term); water pump pliers (British and European usage, from their original use adjusting water pump pulleys on old vehicles); tongue-and-groove pliers or groove-joint pliers (technical US description of the adjustment mechanism); channel-lock pliers or Channellocks (US — Channellock is a brand name that became generic, similar to "Hoover" or "Biro"). In Australia, "multigrips" is the correct generic term. If a supplier or spec sheet says "water pump pliers" or "tongue-and-groove pliers", it is the same product. The adjustment mechanism uses a set of grooves (the "channel" in Channellock) that allow the pivot to be set at multiple positions. Pushing the lower handle forward while the jaws are open advances the pivot position and widens the jaw opening. In most designs, the jaws remain parallel or near-parallel across the adjustment range — which is the key advantage over slip joint pliers for gripping hex fittings and pipe without rounding. Straight jaw vs angled jaw Multigrip pliers come in two jaw configurations: Straight jaw (flat jaw) — jaws are parallel to the handle axis. Better for gripping flat stock, hex nuts, and fittings where you need to hold a specific orientation. Knipex Pliers Wrench is the premium straight-jaw design with smooth jaws (no serrations). Angled jaw (Cobra/standard) — jaws are angled approximately 45° to the handle axis. Provides better access to pipe and fittings in confined locations; the standard configuration for plumbing and general mechanical work. Knipex Cobra is the professional benchmark for this type. For general-purpose mechanical and maintenance use in Australia, a 250mm angled-jaw multigrip covers the majority of applications. A 180mm is useful for confined spaces; a 300mm+ for heavy pipework and large fittings. Locking pliers Locking pliers grip a workpiece and lock in place using an over-centre cam mechanism in the handle. Once set and locked, they hold the workpiece without sustained hand pressure — freeing both hands or holding a part in position while another operation is performed. The adjustment screw in the lower handle sets the jaw width; the upper handle operates the lock-release mechanism. They are called locking pliers generically in Australia. Brand names in common use include Vise-Grips (Irwin — the original brand, now widely used as a generic term), Mole grips (UK/Commonwealth brand name for the same tool — still used in Australian trade speech), and LockJaw (a strong-performing AU-distributed brand available through AIMS Industrial). Irwin Vise-Grip is considered the benchmark for jaw retention and cam mechanism quality. Jaw configurations cover different applications: Curved jaw — the standard configuration. Best for round stock, pipes, and irregular shapes. The most common locking plier in general trade use. Straight jaw (flat jaw) — for flat stock, sheet metal, and square or hex sections. Better grip on hex heads than curved jaw. Long nose locking pliers — tapered jaw for confined spaces and smaller fasteners. Less clamping force than curved jaw. C-clamp locking pliers — deep-throat design that clamps flat surfaces for welding, fabrication, and assembly fixturing. Sheet metal locking pliers — right-angle jaw profile for clamping sheet edges together during welding or fabrication. Locking pliers are particularly effective on seized or rounded fasteners where a spanner cannot grip — the locked jaw bites into remaining material and holds under torque. For dedicated locking plier and clamp applications, see also: Clamping Made Easier and Faster with Lockjaw. ⚠️ Locking pliers are not a spanner substitute for intact fasteners. On undamaged hex heads, a correctly sized spanner or socket applies torque to the full flat face. Locking pliers apply torque through jaw serrations biting into corners — which rounds the head under repeated use. Reserve locking pliers for damaged fasteners, clamping, and holding tasks. Side cutters (diagonal cutters) Side cutters is the dominant Australian term. "Diagonal cutters" and "diagonal pliers" are correct technical names also used in Australian catalogues. "Dykes" is older trade slang still heard occasionally in workshops. The tool is the same: cutting jaws set at an angle to the tool's axis, with hardened cutting edges that shear wire and cable by cutting across it rather than by a chopping or anvil action. The offset jaw geometry allows the tool to be used flush against a surface — cutting cable ties, wire, and soft rod at or near the surface without the handle fouling. This is the most common cutting plier in electrical, automotive, and general maintenance work. Side cutters vs flush cutters Standard side cutters leave a small angled tip on the cut end — the bevel of the cutting edge means the cut is not perpendicular to the wire axis. Flush cutters (also called flush cut pliers or micro cutters) have a flat face on one jaw that produces a cut very close to perpendicular — leaving minimal tip projection. Flush cutters are used in electronics, PCB work, and precision wire work where a projecting tip would snag or short against adjacent conductors. They are softer tools — designed for fine copper wire, not for the harder cables and cable ties that standard side cutters handle. AU electrician's context Marvel "cross cut" pliers are the best-known AU electrician's side cutter — a tool recognised by name in Australian electrical apprentice circles. "Cross cut" refers to the crossed cutting edges ground into the jaw faces, producing a cleaner cut on TPS cable and stranded conductors than a standard diagonal edge. If you're an AU sparky buying your first pair of side cutters, Marvel cross cuts or equivalent (NWS, Knipex) are the correct tool — not a generic hardware-store side cutter. Linesman pliers Linesman pliers — "linesman" in Australian and UK usage, "lineman's pliers" in US usage — are a heavy-duty electrician's combination plier designed for the physically demanding work of pulling wire through conduit, twisting conductors together, and cutting heavy cable. They are larger and heavier than combination pliers, with a flat gripping surface at the jaw tip (for pulling), serrated mid-jaw (for twisting wire), and a hardened side cutter set at the pivot. The flat nose section at the jaw tip is the defining feature: it allows the plier to grab fish tape and pull it through conduit with full hand grip on the handles. Combination pliers cannot do this effectively — the tapered jaw of long nose pliers provides less pulling force and the jaw geometry of standard combination pliers doesn't grip tape securely. Linesman pliers are the correct tool for this specific task. Additional linesman plier functions: Twisting conductors together for splicing — the flat mid-jaw serrations grip and rotate wire cleanly Cutting hard copper conductor and ACSR (aluminium conductor steel-reinforced) overhead cable — linesman pliers use hardened high-leverage cutting edges rated for harder materials than standard combination pliers Gripping and bending conduit knockouts and electrical fittings Standard trade sizes are 200mm and 215mm. Klein 2000 series and NWS linesman pliers are the professional benchmark; Marvel and Channellock are also used in Australian electrical trades. Slip joint pliers Slip joint pliers are the oldest adjustable plier design — the two jaw positions are set by sliding the pivot to one of two holes in the lower arm. The narrow position is for small work; the wide position provides a larger jaw opening for pipe and fittings. That is the full extent of their adjustability. Slip joint pliers have a genuine use case: light household tasks, quick adjustments, and situations where a multigrip would be overkill. In a kitchen-drawer or glovebox context, they earn their keep. In a trade or maintenance environment, they have been almost entirely replaced by multigrip pliers, which offer a wider adjustment range, better jaw parallelism across settings, and more clamping force for the same handle length. The main limitation of slip joints is that the two fixed positions mean the jaws are frequently not parallel on the workpiece — one jaw contacts the corner, the other the flat face, which concentrates force on two small contact points rather than distributing it across the jaw. On hex fittings and round pipe, this rounds the corners quickly. If you already own slip joint pliers and they work for your tasks, there is no reason to replace them. If you are buying pliers for trade or maintenance work, buy multigrips instead — the additional cost is modest and the capability difference is significant. Hose clamp pliers Hose clamp pliers are specialised tools for compressing and releasing spring hose clamps — the type of clamp with two protruding tabs that is compressed to release the clamp's grip on a hose. They are a mandatory tool for any mechanical work involving cooling systems, fuel systems, and vacuum hose removal on vehicles with spring-type OEM hose clamps. The jaws have two rounded pins or pegs that engage the tabs of the spring clamp. Squeezing the handles compresses the clamp against spring tension, which opens the clamp diameter and allows the hose to be moved off the fitting. Without hose clamp pliers, the only alternative is slipping a screwdriver blade under the clamp tabs — which marks the hose, risks slipping off under tension, and gives no control over where the clamp goes once released. Spring clamp vs screw clamp (Jubilee clip) pliers There are two distinct tools that share the name "hose clamp pliers": Spring hose clamp pliers — the pegged tool described above, for OEM spring clamps. These are single-purpose; they do not work on screw-type clamps. Hose clamp installation pliers (Jubilee clip pliers) — a different tool, used to position and tighten worm-drive screw clamps (the type with a screw band, generically called Jubilee clips in Australia). These are offset-jaw pliers designed to reach into confined engine-bay locations where a screwdriver or nut driver won't fit. Not the same tool. If you are replacing OEM spring clamps in a modern vehicle's cooling system, you need spring hose clamp pliers. If you are fitting aftermarket screw clamps in tight locations, you may benefit from offset hose clamp installation pliers. The two are not interchangeable. Crimping pliers Crimping pliers deform a metal sleeve (a crimp ferrule or terminal) around a wire or conductor to make a permanent mechanical and electrical connection. The crimp replaces soldering in most automotive, marine, and industrial wiring applications — it is faster, more consistent, and does not introduce thermal stress to the conductor. Key crimping plier types in AU trade use: Insulated terminal crimpers — crimp colour-coded insulated connectors (red/blue/yellow). The die profiles are matched to the terminal sizes. These are the most common electrician's and auto electrician's crimping plier. Ferrule crimpers (bootlace ferrule crimpers) — crimp copper ferrule sleeves onto stranded conductors before inserting into screw terminals. Essential for switchboard wiring — ferrules prevent strand splaying and ensure a solid, consistent connection in terminal blocks. Ratcheting ferrule crimpers produce the correct hexagonal or quadrilateral crimp profile consistently. Ratchet crimpers — any crimping plier with a ratchet mechanism that prevents the handles from opening until the crimp cycle is complete. Ensures full crimp pressure is applied every time; eliminates under-crimped connections that can fail under vibration or pull-out load. Coaxial and network cable crimpers — die profiles matched to BNC, RJ45, or RJ11 connectors. A separate specialist tool from terminal and ferrule crimpers. The critical rule with crimping pliers is die-to-terminal matching. The crimp die must match the terminal size and type. Using a mismatched die produces either an over-crimped connection (conductor damaged, terminal cracked) or an under-crimped connection (high resistance, pull-out failure). If the die is not marked for the terminal you are using, it is the wrong tool. Circlip pliers (snap ring pliers) Circlip pliers — also called snap ring pliers — are designed to install and remove circlips (internal or external retaining rings) on shafts and in bores. Internal circlips sit in a groove inside a bore; external circlips sit in a groove on the outside of a shaft. The two types require opposite jaw actions: internal circlip pliers expand the ring to fit the bore; external circlip pliers compress the ring to fit the shaft groove. Circlip pliers are available in fixed-tip and interchangeable-tip designs, with straight or 45°/90° angled tips for access in different orientations. For the full guide to circlip pliers — types, tip selection, internal vs external, and correct technique — see the AIMS Industrial Circlip Pliers Guide. Fencing pliers Fencing pliers are a distinctly Australian and rural tool — a multi-function instrument designed specifically for wire fencing work. They are not general-purpose pliers that happen to be used on fences; they are engineered for the specific tasks of fencing construction and maintenance, and they do those tasks in ways that no other plier can replicate efficiently. A standard fencing plier combines up to seven functions in a single tool: Wire cutters — heavy-duty cutting edges capable of cutting galvanised high-tensile fencing wire and barbed wire Wire gripping jaws — serrated flat jaws for holding wire under tension while straining or joining Hammer face — a hardened flat face on the head for driving staples into timber posts Staple starter — a notch or slot for positioning a staple before driving it flush Staple puller — a V-notch or claw for extracting old or incorrectly driven staples Wire twister — a slot that grips wire ends for twisting a join by rotating the pliers Wire stretcher — in some designs, a tightening mechanism for straining wire before stapling Popular brands in Australian rural supply include Irwin Vise-Grip, Strainrite, and Gallagher. The 250–260mm size is standard. Hot-dip galvanised or chrome-plated finishes for corrosion resistance in outdoor conditions. If you maintain rural fencing in Australia, fencing pliers are a mandatory addition to a ute toolbox — no collection of general-purpose tools substitutes for a well-made fencing plier when you need to re-strain and re-staple a wire run in a paddock. Plier wrench A plier wrench is an adjustable gripping tool with smooth, parallel jaws that maintain parallelism across the full adjustment range. Unlike multigrip pliers — which have serrated jaws that bite into the workpiece — the plier wrench's smooth flat jaws grip without marking. This is its defining characteristic and the reason for its premium positioning. The Knipex Pliers Wrench (86-series) is the benchmark product in this category and the only widely available plier wrench in the Australian professional tool market. The adjustment mechanism is a push-button ratchet that steps through jaw-opening positions — no lever or groove sliding; the jaw locks each time the button is released. The parallel jaw geometry means it applies force like a spanner rather than like a conventional plier: full flat-face contact rather than jaw edge or serration contact. Use cases for the plier wrench: Chrome fittings, polished pipe, and plated fasteners where serration marks are unacceptable Hex flats where a correctly sized spanner is not available — the plier wrench provides spanner-equivalent grip without the rounding risk of serrated-jaw multigrips Odd-size fasteners and fittings outside standard spanner ranges High-end plumbing work where fitting surfaces must not be damaged The plier wrench does not replace multigrip pliers for pipework — the smooth jaw does not grip pipe effectively under high torque. It complements multigrips by covering the applications where jaw marking is not acceptable. For a professional mechanic or plumber, a 180mm or 250mm Knipex Pliers Wrench is a tool that justifies its cost quickly in avoided rework and fitting replacement. Plier selection guide The table below gives the correct plier type for common Australian trade and maintenance tasks. For tasks not listed, apply the principle: gripping round or irregular shapes → multigrip; cutting wire → side cutters or linesman; confined access → long nose; marked surfaces → plier wrench; release spring clamps → hose clamp pliers. Task Correct plier type Notes General electrical work — gripping, bending, cutting light wire Combination pliers VDE insulated for live work. 180mm standard size. Reaching into confined spaces — terminals, behind panels Long nose / needle nose pliers Bent nose if access angle requires it. VDE if live electrical. Gripping pipe, fittings, irregular shapes, large fasteners Multigrip pliers 250mm angled jaw covers most applications. Knipex Cobra is benchmark. Gripping polished fittings, chrome pipe, hex flats without marking Plier wrench Knipex 86-series. Smooth parallel jaws. Does not mark surfaces. Cutting TPS cable, wire, cable ties Side cutters (diagonal cutters) Marvel cross cuts for AU electrical. Standard offset for general trade. Cutting precision electronics wire close to board Flush cutters Not side cutters — flush cutters leave minimal projection and will not rip pads. Pulling fish tape through conduit, twisting conductors, cutting heavy cable Linesman pliers 200–215mm. Not a substitute for combination pliers in confined spaces. Seized or rounded fastener — gripping and turning Locking pliers (Vise-Grips) Curved jaw for round stock; straight jaw for hex. Not for intact fasteners. Holding a part in position during welding, fabrication, or assembly Locking pliers — C-clamp type Also sheet metal locking pliers for clamping sheet edges for welding. Releasing spring hose clamps on vehicles Hose clamp pliers (spring type) Pegged jaws engage the clamp tabs. Different tool from Jubilee clip pliers. Crimping insulated terminals on wiring Ratchet terminal crimpers Die must match terminal colour/size. Ratchet type ensures full crimp. Crimping ferrule sleeves on stranded conductors (switchboard wiring) Ferrule crimpers Ratchet type. Different die from terminal crimpers — do not swap. Installing or removing circlips (retaining rings) Circlip / snap ring pliers Internal type for bore circlips; external type for shaft circlips. See full guide. Wire fencing — cutting wire, driving staples, straining fence wire Fencing pliers AU rural standard. Multi-function tool; no general-purpose substitute. Frequently asked questions about pliers What is the difference between combination pliers and multigrip pliers? Combination pliers have a fixed pivot and a single jaw opening — they are general-purpose gripping and cutting pliers used in electrical and maintenance work. Multigrip pliers (also called water pump pliers or tongue-and-groove pliers) have an adjustable pivot with multiple jaw positions, allowing them to grip a wide range of sizes from small fittings to large pipe. Combination pliers are better in confined spaces and for precision wire work; multigrips are better for plumbing, large fittings, and gripping irregular shapes under high torque. The two serve different primary functions and are not direct substitutes for each other. What are multigrip pliers called in the US and UK? "Multigrip pliers" or "multigrips" is the standard Australian term. In the US, the same tool is most commonly called "channel-lock pliers" or "Channellocks" — after the Channellock brand that popularised the design, now used generically. The technical US name is "tongue-and-groove pliers." In the UK and parts of Europe, the tool is often called "water pump pliers" — a name that originates from the tool's use adjusting water pump pulleys on older vehicles. All names refer to the same adjustable jaw plier design. What are side cutters used for? Side cutters — also called diagonal cutters or diagonal pliers — are used to cut wire, cable, cable ties, and soft metal rod by shearing through the material with hardened cutting edges set at an angle to the tool axis. The offset jaw design allows cutting flush against a surface. In Australian electrical work, side cutters are used to cut TPS cable, earth wire, and stranded conductors. In automotive and mechanical work, they cut cable ties, split pins, and lock wire. They are not suitable for cutting hardened steel, spring wire, or piano wire — which requires purpose-designed hard wire cutters. What pliers do electricians use in Australia? The standard Australian electrician's toolkit includes: combination pliers (VDE insulated, 180mm) for general gripping and light wire cutting; side cutters (Marvel cross cuts or equivalent) for cable and wire cutting; long nose pliers (VDE insulated) for terminal connections in confined spaces; linesman pliers for pulling fish tape and heavy wire work; and multigrip pliers for conduit fittings and larger work. VDE 1,000V insulation is required on all pliers used for live electrical work under Australian electrical safety legislation. Preferred brands among AU sparkies include Marvel, Knipex, NWS, and Wiha for insulated tools. What are linesman pliers used for? Linesman pliers are a heavy-duty electrician's combination plier used primarily for pulling fish tape through conduit, twisting conductors together when making splices, and cutting heavy electrical cable. The flat jaw tip provides a secure grip on fish tape — the defining advantage over combination pliers, which cannot grip tape effectively. Linesman pliers are larger and heavier than combination pliers; they are the correct choice for high-force wire pulling tasks, not for delicate terminal work in confined spaces where combination pliers are better suited. The Australian term is "linesman pliers"; the US term is "lineman's pliers." What is the difference between locking pliers and multigrip pliers? Multigrip pliers grip only as long as you squeeze the handles — release pressure and the jaw opens. Locking pliers have an over-centre cam mechanism that locks the jaw at a set opening, maintaining grip without sustained hand pressure. Multigrips are better for plumbing and fitting work where you need to apply and release grip repeatedly across a range of sizes. Locking pliers are better for holding work in position, clamping, and freeing a seized or rounded fastener where maintaining a fixed grip matters more than adjustability. Both are adjustable; the locking mechanism is the key difference. What are hose clamp pliers and do I need them? Hose clamp pliers (spring type) have two pegged jaws that engage the protruding tabs of a spring-type hose clamp. Squeezing the handles compresses the clamp against spring tension, opening the clamp and allowing the hose to be moved or removed. They are essential for any mechanical work on modern vehicles with OEM spring clamps in cooling systems, fuel systems, and vacuum lines. Without them, the alternative is a screwdriver blade under the clamp tab — which is imprecise, risks slipping under tension, and can nick hose material. If you service vehicles, hose clamp pliers are a justified addition to your kit; if you work only on older vehicles or equipment using screw clamps, they are not needed. What is a plier wrench? A plier wrench is an adjustable gripping tool with smooth, parallel jaws that grip without serrations or teeth. The defining characteristic is that the jaws remain parallel across the full adjustment range, providing flat-face contact on the workpiece — similar to a spanner rather than a conventional plier. The Knipex Pliers Wrench (86-series) is the product that defines this category. It does not mark polished or plated surfaces, making it the correct tool for chrome fittings, polished pipe, and hex flats where a standard multigrip would leave jaw marks. It is not a replacement for multigrips — the smooth jaw cannot grip round pipe effectively under high torque. What are the most useful pliers for a tradesperson's toolkit? For a general-purpose Australian trade toolkit, the four most useful plier types are: combination pliers (VDE insulated if electrical work is part of the role); multigrip pliers in 250mm; side cutters; and locking pliers with curved jaw. This set covers the large majority of gripping, bending, cutting, and holding tasks across electrical, mechanical, and maintenance work. Adding long nose pliers covers confined-space terminal work. Adding linesman pliers covers heavy electrical wire pulling. The specific brands worth investing in: Knipex or NWS for combination and long nose pliers; Knipex Cobra for multigrips; Marvel or Knipex for side cutters; Irwin Vise-Grip for locking pliers. Can I use multigrip pliers instead of a spanner on a hex fastener? You can, but it should not be your first choice on an intact fastener. Multigrip pliers apply force through serrated jaw edges contacting the hex corners and flats — the contact area is smaller than a correctly sized spanner, and the serrations bite into the head surface, which damages the corners progressively. On a tight fastener that needs significant torque, the jaw can slip and round the hex head. For intact fasteners, always use the correct spanner or socket first. Reserve multigrips for situations where a spanner is not available, the fastener is already damaged, or the fitting is an odd size that no spanner covers. What does VDE mean on pliers? VDE is the German electrical safety certification mark (Verband der Elektrotechnik, Elektronik und Informationstechnik). On pliers, VDE certification means the handle insulation has been tested and verified to 10,000V AC proof voltage and rated for use at 1,000V AC working voltage. In Australia, VDE-rated insulated pliers are the required standard for working on or near live electrical conductors under state electrical safety legislation. The insulation must cover the full handle surface with no bare metal exposed below the jaw pivot — check that any VDE pliers you buy meet this requirement, as some cheaper tools carry partial insulation that does not meet the standard. Knipex, Wiha, and NWS VDE pliers are the professional standard used by Australian licensed electricians. What are crimping pliers used for? Crimping pliers deform a metal sleeve — called a crimp terminal or ferrule — around an electrical conductor, creating a permanent mechanical and electrical connection. They are used in automotive wiring (insulated terminal connectors), switchboard and industrial wiring (copper ferrule sleeves on stranded wire ends before screw terminal insertion), and communications wiring (coaxial BNC, RJ45). The ratchet mechanism on professional crimping pliers ensures the crimp cycle completes fully before the handles can open — preventing under-crimped connections, which have high resistance and fail under vibration or pull-out. The die profile must match the terminal or ferrule size — using a mismatched die produces either a damaged conductor or a loose connection. What are fencing pliers used for? Fencing pliers are a multi-function tool designed for wire fencing construction and maintenance. In a single tool they combine: heavy-duty wire cutters for galvanised fencing wire and barbed wire; serrated gripping jaws for holding wire under tension; a hammer face for driving staples; a staple starter and puller; and a wire-twisting notch for joining wire ends. They are the standard tool for rural fencing work in Australia — used by landholders, fencing contractors, and anyone who maintains boundary or stock fencing. No combination of general-purpose tools can replace a well-made fencing plier for paddock fencing work efficiently. Pliers from AIMS Industrial AIMS Industrial stocks the full range of trade and industrial pliers — combination pliers, long nose and bent nose pliers, multigrip pliers, locking pliers, side cutters, linesman pliers, hose clamp pliers, crimping pliers, circlip pliers, fencing pliers, and plier wrench types from professional brands including Knipex, Marvel, NWS, Wiha, Irwin Vise-Grip, Channellock, and Kincrome. VDE-insulated ranges for electrical work are stocked across combination, long nose, and linesman plier types. Browse pliers and hand tools at AIMS Industrial Related guides: Circlip Pliers Guide: Internal vs External, Types & Correct Use — full detail on circlip and snap ring plier selection and technique Clamping Made Easier and Faster with Lockjaw — locking pliers and clamps for welding, fabrication, and holding applications Types of Spanners: Complete Guide to Wrench & Spanner Selection — complementary guide for spanner and wrench selection Looking for retaining ring pliers? Our retaining ring pliers range covers the common sizes and brands. For metric and imperial spanner cross-references (M3-M30, AF sizes), see our Spanner Size Chart. For hand winches and cable pullers, see the AIMS manual winches range.
Read moreHex Bolt Guide: Types, Sizes & How to Choose
What is a hex bolt? A hex bolt is a threaded fastener with a six-sided head, tightened with a spanner or socket. It is the workhorse fastener of structural steel, machinery, and general construction. In Australia, hex bolts are most commonly metric (M-series, sized by shank diameter — M6, M8, M10, M12 etc.) and supplied to AS 1110, AS 1111, or AS/NZS 1252 depending on strength grade. What does M8 mean on a bolt? M8 means the bolt has an 8mm shank diameter. The thread pitch is 1.25mm coarse (standard) or 1.0mm fine. M8 bolts take a 13mm spanner or socket across flats. What does M6 mean on a bolt? M6 means the bolt has a 6mm shank diameter. The thread pitch is 1.0mm coarse or 0.75mm fine. M6 bolts take a 10mm spanner or socket across flats. The wrong bolt for an application rarely fails immediately. It fails under load, under vibration, or after a season of outdoor exposure — at which point the joint is compromised, the bolt is difficult to remove, and the cost of the mistake is far higher than the cost of specifying correctly. The most common errors are not dramatic: a full-thread bolt used in a shear joint; a zinc-plated bolt in a coastal application; a coach bolt where a coach screw was needed. Each is avoidable with basic knowledge of what these fasteners are designed to do. This guide covers hex bolt anatomy, the critical partial-thread versus full-thread distinction, the standard metric sizes and spanner sizes, finishes, and the closely related fastener types — coach bolts, flange bolts, and coach screws — that are frequently confused with hex bolts in Australian trade and industrial practice. For detailed information on bolt grades (4.6, 8.8, 10.9, 12.9) and the torque reference chart, see the AIMS Industrial Bolt Grade Chart. Need another reference chart? Browse the full AIMS Engineering Reference Charts library — drill bit sizes, tap drill, torque, viscosity, GD&T, AS/NZS standards and more. What is a hex bolt? A hex bolt is a threaded fastener with a hexagonal head and a cylindrical shank. The head has six flat faces — "hex" from the Greek for six — which accept a spanner, socket, or ring spanner for tightening and loosening. The shank is partially or fully threaded, and in normal use the bolt passes through unthreaded clearance holes in the joined material and is secured by a nut on the opposite side. The key components of a hex bolt are: Head — hexagonal, provides the bearing surface and the wrench engagement. Head dimensions (across flats, across corners, head height) are standardised per ISO 4014/4017 and DIN 931/933. Shank — the body of the bolt. In a partial-thread bolt, the shank has an unthreaded section (the grip length) directly under the head, followed by a threaded section. In a full-thread bolt, the thread runs the entire length. Grip length — the unthreaded shank length. In a correctly designed bolted joint, the grip length equals the combined thickness of the joined materials, so the shear plane falls in the unthreaded shank rather than the threaded section. Thread — metric coarse thread is the AU standard for general fastening. Fine thread is available for vibration-critical or precision applications. Thread length — for partial-thread bolts, the thread occupies approximately the last 2d + 6mm of bolt length (for bolts up to 125mm). A full-thread bolt has thread to the head. Hex bolts are the most common heavy fastener type in Australian industrial, structural, and mechanical applications. They are dimensioned under the ISO 4014 (partial thread) and ISO 4017 (full thread) international standards, also designated DIN 931 and DIN 933 respectively — both designations appear on Australian supplier packaging. Partial thread vs full thread hex bolts This is the most consequential distinction in hex bolt selection and the one most frequently ignored when ordering. Partial thread and full thread bolts look almost identical and are supplied in the same sizes — but their structural behaviour under shear loading is fundamentally different. Partial thread (DIN 931 / ISO 4014) The partial-thread hex bolt — also called a hex set bolt, hex bolt, or hex set screw (partially threaded) — has an unthreaded shank beneath the head. The thread occupies only the end portion of the bolt. When this bolt is correctly sized for the joint, the grip length equals the joint thickness, and the threaded section extends into the nut beyond the joint. The shear plane — the plane along which shear forces act — falls in the unthreaded shank. The unthreaded shank is the full nominal diameter and has no stress concentration from thread roots. It provides the maximum cross-sectional area for resisting shear forces, and the smooth shank surface allows precise location of the joined components. Partial thread hex bolts are the correct choice for structural steel connections, machinery bases, flanges, and any bolted joint designed to carry shear or combined shear-and-tension loading. Full thread (DIN 933 / ISO 4017) The full-thread hex bolt — also called a hex set bolt (fully threaded) or hex set screw — has thread running the entire length from head to tip. There is no unthreaded shank. Full thread bolts are the correct choice when maximum thread engagement is the design requirement: bolting into tapped holes (no nut), through-bolting in applications where the shear plane must be avoided, or where joint movement during assembly requires full thread adjustment. In a through-bolting application under shear load, a full-thread bolt places the thread roots — points of stress concentration — at the shear plane. Thread roots reduce the effective cross-sectional area compared to the unthreaded shank of a partial-thread bolt of the same nominal diameter. For shear-loaded joints, this is a design weakness. ⚠️ The ordering trap: Full-thread bolts are often cheaper per unit and more readily available from trade counters. Many people order them by default without checking whether the application requires a partial-thread shank. In shear-loaded joints — machinery mounts, structural steel connections, flanges — this is incorrect specification. If the engineering drawing or OEM specification calls for a hex bolt without specifying full thread, the assumption is partial thread (ISO 4014 / DIN 931). Partial thread vs full thread — comparison Property Partial thread (DIN 931 / ISO 4014) Full thread (DIN 933 / ISO 4017) Also called Hex bolt, hex set bolt (p/t), set screw (p/t) Hex set bolt (f/t), hex set screw, hex cap screw Shank Unthreaded grip length + threaded end Thread to head — no unthreaded shank Shear plane Falls in unthreaded shank — maximum area Falls in threaded section — reduced area, stress concentrations Best for Structural steel, machinery, flanges, shear/tension joints Tapped holes, maximum thread engagement, clamping applications Standard ISO 4014 / DIN 931 ISO 4017 / DIN 933 Common finish Zinc plate, HDG, plain Zinc plate, stainless, plain Hex bolt sizes: dimensions and spanner chart Metric coarse thread is the standard in Australian industrial and construction applications. The table below gives the key dimensions for metric hex bolts to ISO 4014 / ISO 4017 (DIN 931 / DIN 933) from M6 to M36 — the range covering the vast majority of AU trade and industrial fastening. These values apply to both partial-thread and full-thread hex bolts of the same nominal size. "Across flats" (AF) is the dimension across opposite flat faces of the head — the size of spanner or socket required. "Across corners" (AC) is the maximum width across the hex head corners, relevant for clearance. "Head height" (k) is the height of the head. Nominal size Coarse pitch AF — across flats (spanner size) AC — across corners Head height (k) Notes M6 1.0 mm 10 mm 11.5 mm 4.0 mm Light fittings, guards, covers M8 1.25 mm 13 mm 15.0 mm 5.3 mm Light machinery, electrical panels M10 1.5 mm 17 mm 19.6 mm 6.4 mm General mechanical — very common M12 1.75 mm 19 mm 21.9 mm 7.5 mm Structural, motor bases, flanges M14 2.0 mm 22 mm 25.4 mm 8.8 mm Less common — check application M16 2.0 mm 24 mm 27.7 mm 10.0 mm Structural steel connections M20 2.5 mm 30 mm 34.6 mm 12.5 mm Heavy structural, base plates M24 3.0 mm 36 mm 41.6 mm 15.0 mm Heavy structural, AS 4100 connections M27 3.0 mm 41 mm 47.3 mm 17.0 mm Slip-critical connections, heavy equipment M30 3.5 mm 46 mm 53.1 mm 18.7 mm Heavy industrial, pressure equipment M36 4.0 mm 55 mm 63.5 mm 22.5 mm Very heavy structural, crane components The spanner (AF) size is what you order tooling against. M10 takes a 17mm spanner; M12 takes a 19mm; M16 takes a 24mm. These are the sizes to verify before starting a job on unfamiliar equipment — the wrong spanner size rounds the head corners, making removal progressively more difficult. Fine thread variants Fine-thread metric hex bolts are available for the same nominal diameters but with a smaller thread pitch (e.g., M12 × 1.25 vs M12 × 1.75 coarse). Fine thread develops approximately 5–10% higher preload at the same torque and offers better vibration resistance. Fine-thread bolts are used in automotive applications (suspension components, engine fasteners), precision machinery, and any application where vibration loosening of coarse thread is a concern. Do not mix coarse and fine thread in the same joint — the threads are not interchangeable. How to measure a hex bolt Hex bolt size is specified as nominal diameter × length (e.g., M12 × 75). Length is measured from under the head to the tip — the full shank length including the threaded portion. The head is not included in the length measurement. To identify an existing bolt: measure the shank diameter with calipers (the nominal diameter), count the thread peaks per 10mm to determine pitch, and measure from under the head to the tip for length. Hex bolt grades Hex bolt grade determines the strength — specifically the tensile and yield strength of the fastener material. The metric property class system runs from 4.6 (mild steel, general purpose) through 8.8 (high tensile standard) to 12.9 (maximum strength alloy steel). The numbers encode strength directly: for grade 8.8, the first number × 100 = 800 MPa nominal tensile strength; both numbers × 10 = 640 MPa minimum yield strength. For Australian trade and industrial work: Grade 4.6 — general hardware, non-structural, light-duty. Mild steel, no heat treatment. Grade 8.8 — the standard high-tensile grade. Minimum for structural steel connections under AS 4100. Suitable for machinery bases, flanges, motor mounts, and most industrial fastening. Grade 10.9 — higher clamping force, used in automotive powertrain, slip-critical structural connections, high-load applications. Do not hot-dip galvanise grade 10.9. Grade 12.9 — maximum strength. Cylinder heads, hydraulic equipment, precision clamping. Brittle under shock loading; handle and install with care. ℹ Full grade detail: For the complete metric property class table (4.6 to 12.9), imperial SAE grades, stainless steel grades (A2-70, A4-80), head marking identification, and the M6–M36 torque reference chart, see the AIMS Industrial Bolt Grade Chart. Hex bolt finishes Bolt finish determines corrosion resistance in service. Selecting the wrong finish is a common error — and in structural or outdoor applications, it is a maintenance problem that compounds over time. Finish Also called Corrosion resistance Best for Limitations Plain / uncoated Black, bare steel, plain finish None — will rust immediately in wet conditions Indoor, dry environments only; applications where a coating will be applied (paint, grease) Not for outdoor use, wet environments, or any exposure to moisture Zinc plated — clear Electrozinc, zinc plate, zinc clear passivate Moderate — 72–96 hours salt spray Indoor and sheltered outdoor applications; general mechanical and structural in non-aggressive environments Not suitable for marine, coastal splash zones, or chemical environments Zinc plated — yellow Yellow zinc, zinc yellow passivate, zinc yellow dichromate Moderate-good — 120–200 hours salt spray Similar to clear zinc with marginally better corrosion performance; common on grade 8.8 and 10.9 bolts Same outdoor limitations as clear zinc Hot-dip galvanised (HDG) HDG, galvanised, gal bolt High — 500–1,500+ hours salt spray depending on coating thickness Outdoor structural steel, exposed fixings, agricultural, coastal (above splash zone) Not suitable for grade 10.9 or 12.9 — pickling process before galvanising risks hydrogen embrittlement. Galvanised bolt requires galvanised nut (oversize to allow for coating thickness). 304 stainless steel A2 stainless, 304 SS Good — atmospheric and mild environments Food processing, general outdoor, moderate corrosion environments Not for marine immersion, direct saltwater, or chlorinated water — use 316 SS instead 316 stainless steel A4 stainless, 316 SS, marine grade Excellent — chloride and marine environments Marine, coastal (including splash zones), swimming pools, chemical plant Higher cost; not a structural substitute for grade 8.8 in AS 4100 connections — see bolt grade chart for full comparison Black oxide / black phosphate Black finish, black bolts Low — provides rust inhibition only; typically oil-coated Indoor, light corrosion protection; common finish on grade 12.9 (safe processing for high-hardness steel) Not all black bolts are grade 12.9 — always read head markings. Not for outdoor use without additional protection. ⚠️ Hot-dip galvanising and high grades: Grade 10.9 and 12.9 bolts must not be hot-dip galvanised. The acid pickling step that prepares steel for galvanising can induce hydrogen embrittlement in high-hardness fasteners, causing delayed brittle fracture under load. For outdoor corrosion protection of 10.9 and 12.9 bolts, use mechanical zinc plating, geomet coating, or stainless steel alternatives. This is not a guideline — it is a documented failure mode. Bolt vs screw: the technical distinction In precise fastener terminology, a bolt is a fastener designed to pass through clearance holes and be secured by a nut. A screw is a fastener that engages its own mating thread — either in a tapped hole or by creating its own thread in the material (as with a self-tapping screw or coach screw). Applied to hex fasteners: A hex bolt (ISO 4014 / DIN 931 partial thread) passes through unthreaded clearance holes and is secured with a nut. The nut provides the clamping force. A hex set screw or hex cap screw (ISO 4017 / DIN 933 full thread) engages a tapped hole and provides clamping force without a nut. The term "hex set screw" is used on Australian product catalogues for fully-threaded hex fasteners regardless of application. In practice, the terms "hex bolt" and "hex screw" are used interchangeably in most Australian trade contexts — and this is fine for general ordering purposes. The distinction matters when you are checking a specification drawing, verifying against an engineering standard, or selecting between partial-thread and full-thread products from a catalogue. On AIMS Industrial product listings, "hex bolt" generally refers to the partial-thread product and "hex set bolt" or "hex set screw" to the fully-threaded product. For applications where a spanner cannot reach the head — counterbored holes, recessed mountings, machined assemblies — the equivalent fastener is the socket head cap screw (Allen bolt / DIN 912). Driven by an Allen key from above instead of a spanner from the side, socket head cap screws are stocked at higher property classes (Class 12.9 standard) and are the engineering default for precision joints. Choose hex bolts where side clearance and quick-release matter; choose socket head cap screws where compactness, recessed installation, or maximum strength matter. For the full head-shape comparison across hex, cap, button, truss, countersunk and other styles, see our Screw Head Types Guide. Coach bolt (cup head bolt) The coach bolt — formally called a cup head bolt in Australian and New Zealand standards (AS 1390) — is a distinctly different fastener from a hex bolt, designed specifically for timber and timber-to-steel applications. It is called a "carriage bolt" in North America and the UK. The anatomy of a coach bolt distinguishes it immediately from a hex bolt: Cup (dome) head — a shallow, rounded head with no flat faces for a spanner. Once installed, the head cannot be driven or removed from the bolt side — there is nothing for a tool to grip. Square neck — directly beneath the head, a short square section. When the bolt is driven into a timber member, the square neck bites into the wood and prevents rotation as the nut is tightened from the other side. No tool is needed on the bolt head — the square neck locks it. Threaded shank — the remainder of the shank is threaded for its full length. The installation method follows directly from this design: drill a clearance hole through both members, drive the bolt through from the smooth head side, apply a washer and nut on the thread side, and tighten the nut. The square neck locks into the timber as tightening begins, and the result is a tamper-resistant fixing — the head cannot be backed off without access to the nut side. Common applications in Australia Coach bolts are standard fasteners in: Timber decking — connecting deck boards to bearers, fixing handrails Pergolas and outdoor structures — connecting rafters, posts, and beams Fencing — connecting rails to posts, fixing gate hardware Playground equipment and public furniture — the tamper-resistant head limits vandalism Timber framing — connecting timber to steel or timber to timber in structural applications The dominant sizes in Australian trade are M10 and M12, in lengths from 50mm to 200mm. Hot-dip galvanised finish (grade 4.6 UTS to AS 1390) is the standard for outdoor structural applications. Zinc-plated versions are available for sheltered indoor use. Stainless steel (316 SS) is specified for coastal or marine environments. ℹ AU terminology: The formal name in AS 1390 is "cup head bolt." In practice, Australian tradespeople and trade suppliers consistently use "coach bolt." Both terms refer to the same fastener. Do not confuse coach bolt with coach screw — a coach screw is a different fastener with a hex head and a lag thread that screws directly into timber without a nut (see below). Hex flange bolt A hex flange bolt (or flanged hex bolt) has a standard hexagonal head combined with an integrated washer-like flange at the base of the head. The flange is an integral part of the forging — it cannot be removed. Its purpose is to distribute the clamping load over a larger bearing area, eliminating the need for a separate washer in most applications. Serrated vs plain flange Two variants exist: Serrated (or serrated flange bolt) — the underside of the flange has radial serrations that bite into the mating surface when the bolt is tightened. The serrations lock against loosening under vibration — the bolt cannot rotate backward without overcoming the mechanical engagement of the serrations. This is the dominant type for automotive, plant equipment, and any application subject to vibration or cyclic loading. Plain flange bolt — the flange underside is smooth. Provides load distribution without the locking action. Used where the serrated version would damage a surface coating or where freedom of movement is required. Hex flange bolts are extensively used in automotive and engine-related fastening (exhaust manifolds, engine covers, transmission housings), agricultural machinery, and general equipment where separate washers would be lost during assembly or servicing. In the AIMS Industrial range, hex flanged bolts are available in class 8.8 and 10.9, both zinc-plated and metric fine thread variants for demanding vibration applications. Coach screw (hex head lag screw) A coach screw is a heavy-duty threaded fastener with a hexagonal head and a coarse lag thread designed to cut into and grip timber or other soft materials directly — without a nut. It is not a bolt. The thread is a wood-screw type thread (coarser pitch, sharper thread form than a machine thread), and the screw is driven into a pre-drilled pilot hole by turning the hex head with a spanner or socket. Coach screws are covered by AS/NZS 1393, which specifies mechanical requirements for screws with ISO hexagon heads for use in timber. They are also called "lag screws" or "lag bolts" in North American usage — these terms mean the same fastener. Coach screw vs coach bolt — the confusion These are the two most commonly confused fasteners in Australian timber construction and renovation work: Feature Coach screw (hex head lag screw) Coach bolt (cup head bolt) Head shape Hexagonal (flat faces for spanner) Round dome (no flat faces) Thread type Lag/wood thread — coarse, for direct timber engagement Machine thread — requires a nut Nut required? No — threads directly into timber Yes — nut on back side of joint Installation Drill pilot hole, drive with spanner into timber Drill clearance hole, insert bolt, apply nut from back Best for Timber-to-timber or timber-to-steel one-sided access; fence posts, joist hangers, pergola beams Timber-to-timber through-bolting; structural connections requiring through-bolt clamping force Removable from bolt side? Yes — hex head can be driven both directions No — round head cannot be gripped; access required from nut side The practical rule: if you have access from one side only and you are fixing into timber, use a coach screw. If you have access from both sides and need through-bolt clamping, use a coach bolt. Hex bolt selection guide The table below summarises which fastener type and grade to specify for common Australian trade and industrial applications. These are starting-point recommendations — always verify against design specifications and relevant standards where safety-critical connections are involved. Application Fastener type Grade Finish Notes General machinery frames, guards, covers Hex bolt (partial thread) 8.8 Zinc plate 8.8 preferred over 4.6 where vibration is present Structural steel connections (AS 4100) Hex bolt or structural assembly (K0/K1) 8.8 minimum HDG or zinc Grade 4.6 only in bearing joints per engineer; slip-critical joints: 8.8 or 10.9 Motor flanges, base plates, mechanical mounts Hex bolt (partial thread) 8.8 Zinc plate or plain Partial thread to ensure shear plane in shank Automotive powertrain fasteners Hex bolt (partial or full as specified) 10.9 (OEM spec) Zinc or black Always use OEM grade and torque — not negotiable Tapped hole assembly (no nut) Hex set screw (full thread) 8.8 Zinc plate Full thread maximises thread engagement in tapped hole Vibrating equipment, engine covers Hex flange serrated bolt 8.8 or 10.9 Zinc Serrated flange resists vibration loosening without separate locking washer Timber decking, pergolas, outdoor structures Coach bolt (cup head bolt) 4.6 UTS (AS 1390) HDG M10 or M12 dominant; stainless for coastal/marine Fence posts, joist hangers, one-sided timber fixing Coach screw (lag screw) 4.6 or 8.8 HDG or zinc Pilot hole required; size per AS/NZS 1393 Food processing, mild corrosive environments Hex bolt (partial or full) A2-70 (304 SS) 304 stainless A4-70 (316 SS) if chloride exposure present Coastal, marine, swimming pool Hex bolt (partial or full) A4-80 (316 SS) 316 stainless Do not use 304 SS in direct saltwater or chlorinated environments Exposed outdoor structural — agricultural, civil Hex bolt (partial thread) 8.8 HDG HDG safe for 8.8; do not HDG grade 10.9 or 12.9 Australian standards for hex bolts The key standards governing hex bolt specification in Australia are: AS/NZS 4291.1 — Mechanical properties of fasteners: bolts, screws and studs. The Australian and New Zealand adoption of ISO 898-1. Governs metric property classes 4.6 to 12.9. AS 1110 series — Dimensions and tolerances for metric hex bolts (AS 1110.1 for full thread, AS 1110.2 for partial thread). These establish the head dimensions, thread lengths, and tolerances that apply to AU-market hex bolts. AS 4100 — Steel Structures. The governing standard for structural steel connections in Australia. Specifies minimum fastener grades (8.8 for high-strength connections) and installation requirements. Bolt assemblies for AS 4100 structural connections are supplied as K0 or K1 assemblies (bolt + nut + washers). AS 1390 — Cup head bolts (coach bolts). Governs cup head bolt dimensions and grades. AS/NZS 1393 — Coach screws with ISO hexagon heads. Governs coach screw mechanical requirements for timber applications. Frequently asked questions about hex bolts What is the difference between a hex bolt and a hex screw? Technically, a hex bolt passes through unthreaded clearance holes and is secured with a nut; a hex screw engages a tapped hole directly without a nut. In Australian practice, the terms are often used interchangeably. The practical distinction that matters for ordering: "hex bolt" typically refers to a partial-thread fastener (ISO 4014 / DIN 931) designed for through-bolting with a nut, while "hex set bolt" or "hex set screw" refers to a full-thread fastener (ISO 4017 / DIN 933) used in tapped holes or for full thread engagement. Check which you need before ordering. What is the difference between partial thread and full thread hex bolts? A partial-thread hex bolt (DIN 931 / ISO 4014) has an unthreaded shank section between the head and the threaded end. When correctly sized, the shear plane falls in the smooth shank — which provides full cross-sectional area and no stress concentrations. A full-thread bolt (DIN 933 / ISO 4017) has thread to the head, maximising thread engagement but placing thread roots (stress concentrations) at the shear plane. Partial thread is correct for structural joints, machinery, and flanges under shear or combined loading. Full thread is correct for tapped-hole assemblies and applications requiring maximum thread engagement. What size spanner do I need for common metric hex bolts? The spanner size matches the AF (across flats) dimension of the bolt head. Standard metric coarse: M8 = 13mm; M10 = 17mm; M12 = 19mm; M16 = 24mm; M20 = 30mm; M24 = 36mm; M30 = 46mm; M36 = 55mm. These are the same across ISO 4014 and ISO 4017 bolts of the same nominal size. For M6: 10mm. Always verify against the actual bolt when working on unfamiliar equipment — some imported equipment uses non-standard head dimensions. What is the difference between a coach bolt and a hex bolt in Australia? A coach bolt (formally "cup head bolt" per AS 1390) has a round dome head with no flat faces and a square neck below the head. It passes through both members and is secured with a nut — the square neck locks into timber to prevent rotation during tightening. It is used in timber-to-timber and timber-to-steel applications (decking, pergolas, fencing). A hex bolt has a six-flat hexagonal head that is tightened from the bolt side with a spanner or socket. Hex bolts are used in metal-to-metal joints, machinery, and structural steel connections where tool access to the bolt head is available. What is the difference between a coach screw and a coach bolt? A coach screw (also called a lag screw or lag bolt) has a hexagonal head and a coarse lag thread that cuts directly into timber — no nut required. It is driven from the hex head side with a spanner or socket into a pre-drilled pilot hole. A coach bolt has a dome head and machine thread, requires a nut, and passes through a clearance hole in both members. Use a coach screw when you have one-sided access and are fixing into timber. Use a coach bolt when you have access from both sides and need through-bolt clamping force. These are frequently confused but are not interchangeable. What is a hex flange bolt and when should I use one? A hex flange bolt has an integrated flange at the base of the head that acts as a built-in washer — distributing the clamping load over a larger bearing area. The serrated flange variant has radial serrations on the underside that bite into the mating surface, locking against vibration loosening without a separate locking washer. Use hex flange bolts where vibration loosening is a concern (automotive, engine-related, agricultural machinery) or where handling of separate washers during assembly is impractical. Plain flange bolts are used where serrations would damage a surface coating. What is the difference between zinc plated and hot-dip galvanised hex bolts? Zinc-plated bolts have a thin (5–15 micron) electroplated zinc coating applied by electrochemical deposition. This provides moderate corrosion resistance (typically 72–200 hours salt spray depending on clear or yellow passivate) and is suitable for indoor and sheltered outdoor use. Hot-dip galvanised (HDG) bolts are immersed in molten zinc, producing a thicker (45–85 micron) metallurgically bonded coating with substantially greater corrosion resistance — suited to exposed outdoor structural use, agriculture, and coastal environments above the splash zone. HDG bolts require oversize nuts (galvanised nuts) to accommodate the coating thickness. Critical restriction: do not hot-dip galvanise grade 10.9 or 12.9 bolts. Can stainless steel hex bolts replace grade 8.8 high tensile bolts in structural connections? Not in AS 4100 structural steel connections, which require carbon or alloy steel fasteners. Standard stainless grades (A2-70 at 700 MPa, A4-70 at 700 MPa) fall below grade 8.8's 800 MPa tensile strength. Even A2-80 or A4-80 at 800 MPa are not approved substitutes in AS 4100 connections, which also require certified yield strength, hardness, and installation torque specific to property class steel. For non-structural applications where corrosion resistance is the primary requirement, stainless is correct — but verify the strength class meets the load requirement before specifying. What is DIN 931 and how is it different from DIN 933? DIN 931 (now aligned with ISO 4014) is the German/international standard for partial-thread metric hex bolts. DIN 933 (ISO 4017) is the equivalent standard for full-thread hex bolts (hex set screws). Both designations still appear widely on product packaging and catalogue descriptions in Australia. DIN 931 = partial thread; DIN 933 = full thread. When a product is listed as "DIN 931" it has an unthreaded shank section; "DIN 933" has thread to the head. If the listing shows only a bolt size and grade with no DIN/ISO reference, confirm with the supplier whether it is partial or full thread before ordering. How do I measure a hex bolt correctly? A hex bolt is sized by nominal diameter and length. Diameter: measure across the shank (not the thread peaks) with calipers — this is the nominal metric size (e.g., 10mm = M10). Length: measure from the underside of the head to the tip of the bolt — the head is not included. A bolt marked M12 × 75 has a 12mm shank diameter and is 75mm long from under the head to the tip. To confirm thread pitch: count thread peaks over exactly 10mm of thread length with a rule — 6 peaks in 10mm = 1.5mm pitch (M10 coarse); 5–6 peaks in 10mm = 1.75mm pitch (M12 coarse). What is a "cup head bolt" in Australia? Cup head bolt is the formal Australian and New Zealand name, per AS 1390, for the fastener widely known as a coach bolt or carriage bolt. The name comes from the shallow cup-shaped (dome) head. All three names — cup head bolt, coach bolt, and carriage bolt — refer to the same fastener: dome head, square neck, machine thread, requires a nut. In trade practice, "coach bolt" is the most common term in Australian hardware and trade supply. "Cup head bolt" appears in formal specifications and AS 1390 product descriptions. What thread pitch does an M12 coarse hex bolt have? M12 coarse thread has a pitch of 1.75mm — meaning each full thread revolution advances the fastener 1.75mm. This is the standard pitch for M12 in ISO metric coarse thread series and is the default for general-purpose M12 hex bolts in Australia unless the product is specifically marked as fine thread (M12 × 1.25 or M12 × 1.5). To confirm: run a 19mm spanner across the M12 bolt head and count 5–6 thread peaks in 10mm of thread length. What is the minimum bolt grade for structural steel connections in Australia? AS 4100 (Steel Structures) specifies grade 8.8 as the minimum for high-strength structural connections in Australian steel structures. Grade 4.6 commercial bolts are permitted only in specific bearing-type connections as detailed by the structural engineer of record, and only where explicitly specified. Friction-type (slip-critical) connections require grade 8.8 or 10.9, installed to the specified proof load or snug-tight condition per AS 4100 requirements. Substituting a lower grade without engineering review is not permitted in AS 4100 structural work. See the AIMS Industrial Bolt Grade Chart for the full AS 4100 requirements and torque reference data. What's the difference between a hex bolt and a hex screw? A hex bolt has an unthreaded shank under the head with threads only on the lower portion, designed to clamp two pieces together through a clearance hole using a nut. A hex screw is threaded the full length and is designed to thread directly into a tapped hole. Both have hex heads driven by spanners or sockets — the distinction is in the thread length and how they engage the joint. How do you measure a hex bolt size? Hex bolt size is given as diameter × length — for example M10 × 50 means 10mm diameter shank, 50mm long. Length is measured from under the head to the tip of the threads, not including the head itself. The Across Flats measurement on the head determines the spanner or socket size, not the bolt size. M10 bolts use a 17mm spanner. What does the grade mean on a hex bolt head? Grade markings on the head indicate the tensile strength of the bolt. Metric bolts use a number such as 8.8 or 10.9 stamped on the head — higher numbers mean stronger steel. Imperial bolts use radial line markings — three lines for Grade 5, six lines for Grade 8. Grade selection matters for structural connections and any application where the bolt is under tension or shear load. Can I use a hex bolt in timber? Hex bolts work well in timber when used with a washer to spread the clamping load and prevent the head from sinking into the grain. Drill a clearance hole the size of the bolt shank. For loads parallel to the grain or in softer timbers, use a flat washer under both the head and the nut. Coach bolts are often a better choice for timber where the square shoulder under the head sets into the wood to prevent rotation. Hex bolts and fasteners from AIMS Industrial AIMS Industrial stocks the full range of metric and imperial hex bolts across grade 4.6, 8.8, and 10.9 — in zinc-plated, hot-dip galvanised, plain, and stainless steel (304 and 316) finishes. The range includes partial-thread hex bolts, full-thread hex set bolts, hex flange bolts (serrated and plain), cup head (coach) bolts to AS 1390, structural bolt assemblies (K0/K1) to AS 4100, coach screws, and assortment kits for trade and maintenance. Browse bolts at AIMS Industrial Related guides: Bolt Grade Chart: Metric, Imperial & High Tensile Markings Guide — complete grade table (4.6 to 12.9), head markings, and M6–M36 torque reference chart Types of Rivets: Pop Rivets, Blind Rivets, Solid Rivets & How to Choose Tap & Die Guide: Cutting and Repairing Threads Choosing the right tap for the job? Our Tap Types guide covers taper, plug, bottoming, spiral point and spiral flute taps. Match the rivet to the right gun — see rivet tools at AIMS.
Read moreCirclip Pliers Guide: Internal vs External, Types & Correct Use
Circlip pliers are broadly grouped into size classes. Most 4-piece sets fall into the standard range; industrial and mining applications frequently.
Read moreScrewdriver Types Guide: Types, Sizes & Selection
A stripped screw head is not bad luck. It is almost always the result of using the wrong driver — and in most cases the driver looked right. Pozidriv and Phillips screwdrivers appear nearly identical. JIS and Phillips are visually indistinguishable to most people. Use the wrong one under any meaningful torque and the result is a rounded, damaged recess that is now harder to remove than it was to drive. This guide covers every drive type you are likely to encounter in Australian trade and maintenance work, how to identify each one, the correct driver sizes, and the tool types available for different applications. Why getting the drive type right matters Every screw drive system is designed around a specific geometry — the angle of the flanks, the number of contact points, and the degree to which the driver is designed to stay in the recess under load. When you use a driver that does not match that geometry exactly, the contact shifts from the designed bearing surfaces to the edges and corners of the recess. Under torque, those edges deform. Do it once at moderate torque and the damage is minor. Do it repeatedly, or at high torque, and the recess becomes rounded to the point where no driver — not even the correct one — can grip it. The correct driver costs less to buy than the time it takes to extract a stripped fastener. In most cases, the correct driver is the only real fix. This guide will help you identify which one you need before you apply torque, not after. Slotted screwdrivers The slotted drive — a single straight slot across the screw head — is the oldest screw drive system still in widespread use. It is not common in modern construction or manufactured equipment, but it is far from obsolete. You will encounter slotted fasteners regularly in: Electrical switchgear, switchboards and terminal blocks Plumbing fittings and stopcock bodies Older machinery and plant equipment manufactured before cross-head drives became standard Vintage automotive applications Wood screws in older furniture and joinery Slotted screwdrivers are sized by blade width and blade thickness. Common blade widths are 2.5mm, 3mm, 4mm, 5.5mm, and 6.5mm. The blade must fit the slot cleanly — too narrow and it rocks in the slot, concentrating force on the slot corners; too wide and the blade will score the material surrounding the screw head. Common misconception: "Flat head screwdriver" is often used as a generic term for any non-cross screwdriver. In AU trade use, flat head and slotted are the same thing. A flat head screwdriver is not a substitute for a Pozidriv or Phillips — the geometry is wrong and the blade will cam out immediately under any load. Phillips screwdrivers The Phillips drive is the most widely recognised cross-head drive worldwide. It was patented by Henry F. Phillips in 1936 and adopted rapidly by the automotive manufacturing industry in North America, then globally. Phillips fasteners are still the most common cross-head drive in Australian electrical work, light construction, flat-pack furniture from non-European suppliers, and imported equipment from North America and Asia. Phillips sizes Size Blade tip width Common applications PH0 ~3mm Electronics, PCBs, small appliances, eyeglass frames PH1 ~5mm Small screws in electrical accessories, light fixtures, computer hardware PH2 ~6mm The most common size — general construction, appliances, hardware, M3–M5 fasteners PH3 ~8mm Large fasteners, structural timber screws, heavy appliances The PH2 handles the vast majority of everyday Phillips fasteners. A PH1 and PH2 together cover most electrical and general trade work. The cam-out design — a feature, not a flaw Phillips screws are deliberately designed to cam out — to eject the driver from the recess when a certain torque threshold is reached. This was not an oversight in the design. When Phillips developed the drive for automotive assembly lines in the 1930s, the goal was to prevent overtightening. The cam-out meant an air-powered assembly tool would slip rather than strip the screw once it was fully seated. In hand-tightening applications, this design means the Phillips drive has a lower maximum torque than Pozidriv or Torx before slipping. For light-duty fastening this is not a problem. For high-torque applications — structural timber screws, decking, large machine screws — the cam-out becomes a genuine limitation. This is one reason Pozidriv and Torx have largely replaced Phillips in demanding applications. ℹ Using the correct Phillips size matters: A PH2 driver in a PH1 screw will bridge across the recess rather than seating in it. The contact is on the outer edge of the cross, not the full flank — immediate cam-out risk. Always match the driver size to the screw size. If in doubt, the correct driver sits fully into the recess with no rocking. Pozidriv screwdrivers Pozidriv (often abbreviated PZ) was developed in the 1960s as a direct improvement on Phillips, specifically to eliminate cam-out. It is the dominant cross-head drive in European construction and manufacturing, and the standard drive on most modern Australian construction screws including Type 17 point screws, bugle head screws, decking screws, and chipboard screws supplied through Australian hardware and trade suppliers. Pozidriv looks almost identical to Phillips at a glance. The difference is four additional ribs between the arms of the cross, set at 45° to the main cross. These ribs engage corresponding ribs in the screw recess and prevent the driver from camming out — significantly more torque can be applied before slippage occurs. Pozidriv sizes Size Common applications PZ0 Small screws in electrical fittings, electronics PZ1 Fine woodworking screws, small construction screws, M3–M4 range PZ2 The dominant size — most AU construction screws, M5–M8, decking, framing PZ3 Large structural screws, M10 and above PZ2 is the most important size to have. It is the correct driver for the majority of screws sold through Australian trade and hardware suppliers. Identifying a Pozidriv screwdriver On the screwdriver shank or blade, the size is typically stamped as PZ1, PZ2, or PZ3. On the screw head itself, Pozidriv screws have four small radial marks between the arms of the cross. Phillips screws have smooth, uninterrupted arms with no secondary markings. This is the most reliable visual identification method. Phillips vs Pozidriv: the most common mixup in Australian workshops This confusion is responsible for more stripped screws in Australian homes and workshops than any other single factor. The two drives are not interchangeable — using Phillips in Pozidriv (or vice versa) will damage the screw recess, particularly under power-tool torque. The issue is that a Phillips driver will physically fit into a Pozidriv recess. It engages the main cross arms and feels seated. But it does not engage the 45° ribs. Under torque, the mismatch means the driver rides up and out of the recess — stripping the corners of the cross arms in the process. ⚠️ IKEA furniture uses Pozidriv, not Phillips. Most Australians building IKEA furniture reach for a Phillips driver. IKEA screws are PZ2. A Phillips driver will strip them easily, particularly under power-tool torque. Use a PZ2 screwdriver or bit. The difference is immediately apparent — the PZ2 seats firmly and does not slip; the PH2 skates across the recess under load. How to tell which you have: Look at the screw head. Four small radial lines between the cross arms = Pozidriv. No secondary marks = Phillips. Look at the driver. "PZ" prefix on the shank = Pozidriv. "PH" prefix = Phillips. A driver stamped with just a number and no prefix is likely Phillips. Feel the engagement. A correctly matched driver seats fully and feels solid. A mismatched driver rocks slightly in the recess under light pressure. If in doubt on modern AU construction screws, use PZ2. Most timber screws, decking screws, and bugle head screws sold in Australia in the last 20 years are Pozidriv. Phillips is more common in electrical fittings and imported North American or Asian equipment. JIS screwdrivers JIS stands for Japanese Industrial Standard. JIS cross-head fasteners look identical to Phillips fasteners — same cross shape, no obvious external marking on most examples. The difference is internal: the JIS recess has a slightly different flank angle and a tighter fit geometry than Phillips. JIS is the standard fastener drive used on Japanese-manufactured vehicles and motorcycles, and on Japanese appliances and electronics. In the Australian market, this is not a minor consideration. Toyota, Mazda, Honda, Subaru, Mitsubishi, Suzuki, Nissan, and Yamaha all use JIS fasteners extensively throughout their drivetrain, body, and electrical systems. Australia's vehicle fleet is dominated by Japanese makes. Any technician servicing Japanese vehicles without JIS drivers is using Phillips in JIS recesses on every fastener. A Phillips driver will physically fit a JIS screw — which is why the problem goes unrecognised. But the angular mismatch means the Phillips driver bears on the outer corners of the recess rather than the full flank. At high torque (particularly with an impact driver), Phillips in JIS is one of the fastest ways to damage a screw head. JIS drivers sit flush, bear on the full flank, and do not slip. Identifying JIS fasteners JIS screws are technically marked with a small dot or dimple stamped near the cross recess. In practice, this mark is absent on many older JIS fasteners, worn off on used fasteners, or simply too small to see without looking for it specifically. The reliable identification method: if you are working on Japanese-made equipment, assume JIS and use a JIS driver. JIS screwdriver availability in Australia JIS screwdrivers are not stocked widely in general hardware retail. Specialist tool suppliers and online channels are the primary source. Vessel is the most widely recommended brand for JIS — a Japanese manufacturer whose screwdrivers are designed to the original JIS specification. Wiha produces JIS-compatible Picofinish precision screwdrivers for fine work. For automotive maintenance on Japanese vehicles, a JIS set is a worthwhile addition to any tool kit. Torx screwdrivers Torx is a six-point star-shaped drive developed by Camcar Textron in 1967. In Australia it is commonly called a "star head" or "star drive." The six-lobe geometry distributes torque across a larger bearing surface than either Phillips or Pozidriv, and the near-vertical flank angle means Torx does not cam out under any practical torque load. Torx is now the dominant drive in automotive manufacturing, structural construction fasteners, and electronics. If you service modern vehicles — any make, any origin — Torx drivers are not optional. They are also standard on much modern machinery, white goods, and power tools. For the deep-dive on Torx — the full T1 to T100 size chart, External Torx (E-series), Torx Plus (IP/EP), security Torx with centre pin, and how to choose between insert, impact-rated and hand-driver bits — see our dedicated Torx Bit Sizes Guide. Torx T-size reference Size Common applications T6 Precision electronics, wearables, game controllers T8 Laptops, small electronics, some game consoles T10 Hard drives, optical drives, some automotive sensors T15 Computer components, brake callipers on some vehicles T20 Light automotive, electrical accessories, tools T25 Automotive (most common Torx in AU vehicle maintenance — Toyota, Mazda, Subaru, Nissan brake components, trim panels, engine covers) T27 Larger automotive fasteners, some appliances T30 Automotive (engine fasteners, differential covers) T40 Large automotive fasteners, industrial equipment T45–T55 Heavy equipment, CV joints, wheel hubs on some European vehicles T25 is the single most useful Torx to have for general AU automotive maintenance. T20 covers electrical accessories and light components. T27, T30, and T40 are needed for heavier powertrain work. Security Torx (tamper-resistant Torx) Security Torx — also designated TX or TR (tamper-resistant) — has a small pin in the centre of the six-lobe socket. The pin prevents a standard Torx driver from seating in the recess. Security Torx requires a driver with a corresponding hole in the tip. Security Torx is used on public infrastructure fasteners (transit seating, playground equipment, public signage), some electronics (game consoles, some laptops), electrical metering equipment, and increasingly in automotive applications where tamper resistance is specified. A security Torx set is a worthwhile addition to any maintenance toolkit. "Star screwdriver" — the AU terminology In Australian hardware retail and trade conversation, "star screwdriver" and "star driver" consistently mean Torx. This is informal — it is not a product category designation — but it is widely understood. If someone asks for a star screwdriver, a Torx driver is what they need. When buying, look for the "Torx" or "T" designation on the product — "star" alone will not appear on professional tool packaging. Hex screwdrivers Hex drive — also called Allen drive — uses a six-sided (hexagonal) socket in the fastener head. In Australian use, "Allen key" typically refers to the L-shaped bar tool; a hex screwdriver is the same drive in a traditional screwdriver handle, with the hex bit pointing forward. Both engage the same fasteners. Hex fasteners are extremely common in: Machinery and industrial equipment (socket head cap screws, grub screws) Flat-pack furniture — often 4mm or 5mm hex Bicycle components Plumbing fittings (hex socket grub screws in valve bodies) Automotive (engine and drivetrain components, particularly European vehicles) Hex drive sizes in Australian use are primarily metric: 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 8mm, and 10mm are the most common. A few imperial hex sizes (3/32", 1/8", 5/32", 3/16", 1/4") still appear on older Australian plant and agricultural equipment, and on North American vehicles. For screwdriver-form hex tools, the T-handle hex driver provides significantly better torque leverage than an L-key on larger fasteners. Wiha produces quality T-handle and screwdriver-form hex sets in metric sizes. Robertson (square drive) Robertson drive uses a square socket and was invented by Peter Robertson in Canada in 1908. It offers excellent cam-out resistance and is extremely common in Canada, where it is the standard for most construction screws. In Australia, Robertson drive fasteners are uncommon — most AU suppliers do not stock them as a standard product. Where you will encounter Robertson in Australia: woodworking projects from Canadian or American sources, some American-made equipment, and occasionally in specialty fasteners. If you are working with imported North American timber connectors or framing hardware, check for a square recess before reaching for a Phillips. Robertson drivers are sized R1 (smallest) through R4. R2 is the most common size in construction applications. Security and specialty drives Beyond the main drive types, a range of specialty and tamper-resistant drives exist. Most are encountered in specific contexts — consumer electronics, public infrastructure, or legacy equipment. Drive Description Where you'll find it in Australia Pentalobe Five-lobe, rounded flanks. Not interchangeable with any other drive. Requires a specific Pentalobe driver. Apple products — iPhone (since iPhone 4), MacBook base screws. P2 (iPhone) and P5 (MacBook) are the sizes encountered. Tri-wing Three-wing triangular drive. Nintendo products (DS, Switch cartridges), some older Apple products, certain aviation fasteners. Requires a specific tri-wing driver. Spanner / two-hole Two round holes in the screw head. No standard size. Public infrastructure — elevator buttons, electrical panel covers, tamper-resistant cover plates. Requires a specific two-pin spanner screwdriver. Clutch head Bow-tie shaped recess. Two variants: Type A and Type G. Rare in Australia. Found on vintage American vehicles (1940s–60s) and some RV/caravan fitouts. Torq-set Offset cross-point, looks like a rotated Phillips. Aerospace fasteners only. You will not encounter this outside aircraft maintenance. For most trades, Pentalobe and Tri-wing are the only specialty drives likely to appear in general work — Pentalobe on any Apple device repair, Tri-wing on Nintendo hardware. Both require their own dedicated drivers and are not addressable with any standard driver type. Screwdriver tool types Drive type (the recess geometry) and tool type (the handle/mechanism design) are independent variables. Every drive type is available in multiple tool types. Tool type Description Best use Standard manual Fixed blade or bit, straight handle General fastening and removal across all drive types. The baseline tool. Stubby Short blade, short handle — typically under 100mm overall length Confined spaces where a standard-length driver cannot swing or reach. Electricians and panel workers use these regularly. Ratchet Ratcheting mechanism in the handle allows continuous rotation without repositioning grip High-repetition fastening and removal where repositioning the hand repeatedly would be slow or fatiguing. Switchboard work, assembly. Offset Z-shaped or right-angle handle positions the blade perpendicular to the handle axis Fasteners that are completely inaccessible to a straight driver — flush-mounted or recessed positions with no axial clearance. Precision / watchmaker Small diameter handle, often with a spinning top cap for steady rotation under fingertip pressure Electronics, PCB work, instrument repair, eyeglass frames. PH0, PH00, small Torx (T4–T10), and small slotted. Manual impact screwdriver Heavy body designed to be struck with a hammer; converts impact force to rotation Freeing seized or corroded fasteners — particularly JIS and Phillips screws on older Japanese vehicles and motorcycles. The rotational shock often frees fasteners that would strip under steady torque. Electric / cordless screwdriver Battery-powered, low-torque, typically with adjustable clutch Light-duty fastening in joinery, electrical work, and assembly where a full impact driver is excessive. Better torque control than an impact driver for delicate applications. Torque screwdriver Calibrated to click or slip at a specified torque setting Any application where fastener torque must be controlled to a specification — electronics assembly, medical device maintenance, precision engineering. Wiha produces a range of torque screwdrivers from 0.04Nm for fine electronics to 5.0Nm for general assembly. ℹ Impact driver vs impact screwdriver: These are different tools. A manual impact screwdriver is a hand tool struck with a hammer — it converts the impact to rotation and is used to free seized fasteners. An impact driver is a cordless power tool that uses a rotational hammering mechanism to drive fasteners at high torque. The impact driver is a common power tool in Australian construction trades. The manual impact screwdriver is a hand tool used in automotive and motorcycle maintenance. Screwdriver size reference Having the right driver size is as important as having the right drive type. An oversized or undersized driver applies torque to the wrong part of the recess geometry and causes damage even when the drive type is correct. Drive Size Typical screw/fastener range Priority Phillips PH0 M1–M2, electronics, eyeglasses Precision kit Phillips PH1 M2–M3.5, electrical fittings, small appliances High Phillips PH2 M4–M6, general hardware — the most common size in AU Essential Phillips PH3 M7–M8+, large timber screws, heavy appliances Medium Pozidriv PZ1 Fine woodworking screws, small M3–M4 Medium Pozidriv PZ2 Most AU construction, decking, framing screws — dominant size Essential Pozidriv PZ3 Large structural screws M10+ Low–Medium Torx T8 Laptops, electronics, precision equipment Precision kit Torx T20 Light automotive, electrical accessories High Torx T25 Most common Torx in AU automotive — brakes, trim, engine covers Essential Torx T27 Larger automotive fasteners Medium Torx T30 Engine and drivetrain components Medium Torx T40 Heavy automotive and industrial Medium Slotted 4mm blade General electrical switchgear, terminal blocks High Slotted 5.5mm blade Larger electrical fittings, older plant Medium Hex 3–6mm Machinery, flat-pack, cap screws High How to read a screw head and select the right driver Drive style (Phillips, Pozi, Torx, hex socket etc.) and head shape (pan, button, truss, countersunk etc.) are independent decisions. The same head shape — for example a pan head — can be ordered with several different drives. For the full head-shape reference covering pan, button, truss, countersunk, dome, wafer, bugle, hex flange and security heads, see our Screw Head Types Guide. Before applying any driver to an unfamiliar fastener: Identify the drive type by geometry. Count the arms (cross = Phillips, Pozidriv, or JIS; six points = Torx; single line = slotted; six-sided socket = hex). For cross-head drives, look for the 45° radial marks that indicate Pozidriv. Look for a small dot that may indicate JIS. Select the correct drive type. On Japanese equipment, default to JIS. On modern Australian construction screws, default to Pozidriv. On electrical fittings, default to Phillips. If uncertain, look at the marking on an existing known-correct driver nearby. Select the correct size. Seat the driver in the recess without applying torque. It should feel fully engaged with no rocking and no gap between the driver tip and the recess walls. If it rocks, the size is wrong. Apply torque progressively. If the driver begins to cam out or walk, stop immediately — continuing will damage the recess. Reassess the drive type and size before proceeding. Frequently asked questions about screwdriver types What is the difference between Phillips and Pozidriv screwdrivers? Phillips (PH) and Pozidriv (PZ) are both cross-head drives that look nearly identical, but they are not interchangeable. Pozidriv has four additional ribs between the arms of the cross, set at 45°, which engage matching ribs in the screw recess and prevent cam-out. Phillips was designed with shallow-angle flanks that allow the driver to cam out under high torque. Pozidriv can handle significantly more torque without slipping. Most modern Australian construction screws are Pozidriv; most electrical fittings and North American/Asian imported hardware use Phillips. Can I use a Phillips screwdriver on a Pozidriv screw? A Phillips driver will physically fit into a Pozidriv recess but will not engage correctly. The Phillips tip contacts the main cross arms but misses the 45° ribs. Under load, the driver will cam out and round the corners of the recess. For light hand-tightening with minimal torque, the damage is minor. Under power-tool torque, a Phillips driver in a Pozidriv screw will strip the head quickly. Use the correct PZ-sized Pozidriv driver. How do I tell if a screw is Phillips or Pozidriv? Look at the screw head. Pozidriv screws have four small radial lines between the arms of the cross — these correspond to the 45° ribs on the PZ driver. Phillips screws have a plain cross with no secondary markings. If the radial lines are present, the screw is Pozidriv and requires a PZ driver. If the cross is clean with no secondary marks, it is Phillips and requires a PH driver. On very small or worn screws the marks can be difficult to see — use good lighting and magnification if needed. What is a JIS screwdriver and do I need one for Japanese cars? JIS (Japanese Industrial Standard) is a cross-head drive used on Japanese-manufactured vehicles, motorcycles, and appliances. JIS screws look identical to Phillips and have no obvious external marker on most examples. The internal geometry is slightly different — the flank angles are tighter. A Phillips driver fits JIS screws but does not bear on the full flank, creating a cam-out risk under high torque. If you work on Japanese vehicles (Toyota, Honda, Mazda, Subaru, Mitsubishi, Suzuki, Yamaha) or motorcycles, JIS drivers will correctly engage the fasteners that a Phillips driver damages. JIS drivers are available from specialist tool suppliers; Wiha Picofinish precision drivers cover the fine-thread JIS fasteners in electronics and instruments. What does the T-number mean on Torx screwdrivers (T8, T20, T25)? The T-number refers to the diameter of the inscribed circle of the six-point star, in standardised increments. Higher numbers are larger drives. T8 is used in laptops and consumer electronics; T20 in light automotive and electrical accessories; T25 is the most common Torx size in Australian automotive maintenance (Toyota, Mazda, Subaru brake components, trim panels, engine covers); T27, T30, and T40 are used for heavier drivetrain and structural fasteners. Most automotive Torx sets include T20 through T50; most electronics kits include T4 through T15. What is a "star head" screwdriver? In Australian trade and hardware usage, "star head" or "star drive" is an informal name for Torx. The six-lobe geometry looks like a six-pointed star. This is not an official designation — you will not see "star" on professional tool packaging — but it is widely understood. If someone asks for a star driver or star screwdriver, they need a Torx driver. Check the fastener for the T-size number and match the driver accordingly. Why does my Phillips screwdriver keep slipping out of the screw? Three possible causes: (1) Wrong drive type — the screw may be Pozidriv or JIS, not Phillips. Check for the 45° radial marks (Pozidriv) or consider whether it is Japanese equipment (JIS). (2) Wrong size — a PH2 in a PH1 recess bridges across rather than seating fully. The driver must match the screw size. (3) Worn driver tip — Phillips tips wear with use; once the flanks are rounded, the driver cannot grip the recess properly. Replace worn drivers rather than continuing to use them. What screwdriver does IKEA furniture use? IKEA furniture uses Pozidriv screws, predominantly PZ2. Despite this, most Australians reach for a Phillips driver during assembly — Phillips drivers will fit but will strip the IKEA screw heads under power-tool torque. Use a PZ2 Pozidriv screwdriver or bit. The engagement with a correctly matched PZ2 is noticeably more positive than with a Phillips driver. What is a security Torx screwdriver? Security Torx — also called tamper-resistant Torx (TR or TX) — has a small pin in the centre of the six-lobe recess that prevents a standard Torx driver from engaging. A security Torx driver has a corresponding hollow at the tip to clear the centre pin. Security Torx is used on public infrastructure fasteners, game consoles (some models), electrical metering equipment, and some automotive applications. Standard Torx sizes in the T8–T40 range are commonly available in tamper-resistant versions. What is the difference between an impact screwdriver and an impact driver? A manual impact screwdriver is a hand tool struck with a hammer. The body converts the hammer blow into a rotational impulse that can free seized or corroded fasteners — particularly useful on Japanese vehicles where JIS or Phillips screws have corroded in place. An impact driver is a cordless power tool that uses an internal rotational hammering mechanism to drive fasteners at high torque with lower reaction force than a drill. These are entirely different tools. The manual impact screwdriver is a specialised extraction tool; the cordless impact driver is a primary fastening tool for construction and trade work. What is a ratchet screwdriver used for? A ratchet screwdriver uses a ratcheting mechanism in the handle that allows the blade to drive in one direction while the handle moves freely in the other. This means you can maintain your grip and rock the handle back and forth without repositioning — significantly faster for high-repetition work than lifting and repositioning a standard driver. Ratchet screwdrivers are used in switchboard work, assembly work, and any application involving multiple fasteners of the same type. Most ratchet screwdrivers accept interchangeable bits, so one handle covers Phillips, Pozidriv, Torx, slotted, and hex drives. What does "cam out" mean on a screwdriver? Cam-out describes the tendency of a driver to ride up and out of the screw recess under rotational load. It occurs when the angular geometry of the driver flanks causes an upward force component as torque increases. Phillips screws are deliberately designed to cam out at a specific torque — this was a feature for assembly-line manufacturing. Pozidriv, Torx, and Robertson drives have near-vertical flanks that resist cam-out. In practice, cam-out damages the recess — each time the driver jumps out, it rounds the contact surfaces slightly. Repeated cam-out eventually produces a screw that cannot be driven or extracted with any tool. Screwdrivers from AIMS Industrial AIMS Industrial stocks the full Wiha screwdriver range for trade and industrial use — including Picofinish precision drivers (Phillips, Pozidriv, Torx, slotted), SoftFinish insulated VDE 1000V drivers for electrical work, ESD-safe precision sets, torque screwdrivers from 0.04Nm to 5.0Nm, and stubby and ratchet configurations across all common drive types. Browse screwdrivers at AIMS Industrial | Browse screwdriver bits at AIMS Industrial Related guides: Types of Spanners: Complete Guide to Wrench & Spanner Selection Drill Bit Types Guide — choosing the right bit for every material Tap & Die Guide — cutting and repairing threads Need screw pitch gauges? Browse the AIMS range at screw pitch gauges. Pair this with our Metric Bolt Size Guide for the thread pitch, AF dimension and grade options at every common size. People Also Ask — Types of Screwdrivers Q: Why does using the wrong screwdriver type cause problems? Using the wrong drive type — even if it appears to fit — causes cam-out, where the driver tip rides out of the recess under torque. This damages the screw head, making extraction more difficult, and can also damage the screwdriver tip itself. Matching the correct driver profile to the fastener is the single most important principle in screw driving. Q: What is the difference between a Phillips and a Pozidriv screwdriver? Phillips screwdrivers have four simple tapered wings that cam out intentionally under high torque. Pozidriv has additional angled ribs between the four main wings, creating a more positive engagement that resists cam-out significantly better. A Phillips driver can physically fit a Pozidriv head but will cam out and damage the recess under load. Q: What are slotted screwdrivers used for and why are they less common in modern manufacturing? Slotted screwdrivers engage a single straight slot and are the oldest screwdriver type. They are still used in electrical and heritage applications but have largely been displaced by cross-head drives, which are easier to align and drive at higher torque without slipping off the screw head. Q: What is a JIS screwdriver and when do you need one? JIS (Japanese Industrial Standard) screwdrivers look similar to Phillips but have a different tip geometry. They are required for Japanese-manufactured equipment — particularly motorcycles and small engines — where screws were designed to the JIS standard. Using a Phillips driver in a JIS screw causes cam-out and head damage. Q: How do you tell a Phillips screw from a Pozidriv screw? Pozidriv screws have small additional lines (ribs) between the four main cross slots, visible on close inspection. Phillips screws do not have these extra marks. On worn or painted fasteners the markings may be less clear, but a Pozidriv driver tip is visually distinct from a Phillips tip due to its extra set of wings.
Read moreAllen Key & Hex Key Guide
An allen key is one of those tools that every workshop, toolbox, and kitchen drawer seems to have in abundance — yet when you actually need a specific size, the right one is never there. This guide covers every type of allen key, the complete metric and imperial size charts with bolt compatibility, and the mistakes that turn a simple job into a stripped fastener and half a day's grief. Bookmark our Engineering Reference Charts hub for related sizing tables, conversion charts and Australian standard references across 9 topic clusters. What Is an Allen Key? An allen key is an L-shaped bar of hexagonal (six-sided) steel used to drive fasteners with a hexagonal socket in their head — typically socket head cap screws, grub screws, and hex socket button head screws. The hexagonal cross-section engages all six sides of the socket simultaneously, providing better torque transfer and less slippage than a flathead or Phillips driver. The name "allen key" comes from the Allen Manufacturing Company of Hartford, Connecticut, which patented a design for the socket head screw system in the early twentieth century. The trademark became so widespread that "allen key" entered general use as a generic term — a similar story to Biro, Hoover, and Velcro. In Australia, "allen key" is by far the most common term. "Hex key" is the technically correct term and appears in trade catalogues and engineering drawings. "Allen wrench" is the North American equivalent — you will rarely hear it in an Australian workshop. For this guide, allen key and hex key are used interchangeably. They describe the same tool. How the drive system works The hexagonal socket in a screw head is manufactured to a specific across-flats dimension — the distance between two parallel flat faces of the hexagon. The allen key must match this dimension precisely. Too small and the key rocks in the socket; too large and it will not enter. The key engages all six contact points when properly sized, distributing the applied torque evenly. A poorly fitting key concentrates force on two or three contact points and rounds them off — the mechanism by which allen key drives get stripped. Allen Key vs Hex Key vs Allen Wrench: Sorting Out the Terminology All three terms describe the same tool. The distinction is regional and historical, not technical. Allen key — the dominant Australian and UK term. Originated as a trademark, now used generically. What you will ask for at a hardware store in Sydney, Melbourne, or Brisbane. Hex key — the engineering and trade catalogue term. Correctly describes the tool's geometry (hexagonal cross-section). Used in ISO and DIN standards, manufacturer specifications, and tool catalogues. If you are reading a workshop manual or engineering drawing, it will say hex key. Allen wrench — the North American term. Standard terminology in the USA and Canada. Uncommon in Australia — if someone says "allen wrench" in an Australian workshop, they have probably worked in North America or are reading an American manual. In practice, all three terms are understood in any AU industrial or trade context. The size charts, standards, and specifications are identical regardless of which term is used. Types of Allen Keys Five configurations cover the Australian market. Each has a specific use case — the right type depends on access, torque requirement, and frequency of use. 1. L-Shape (Standard) Allen Key The classic configuration: a single piece of hexagonal steel bar bent 90 degrees into an L-shape. One leg is shorter (the drive end) and one is longer (the handle). Reversing the key — driving with the long leg and using the short leg as a handle — gives significantly more torque for initial tightening or breaking loose a fastener. Using the short leg as the drive gives better access in tight spaces and finer feel for seating the fastener. L-shape keys are the most common type in Australian workshops. They are robust, inexpensive, easy to source, and provide excellent torque feel — the direct feedback through the steel bar tells you when the fastener is approaching its limit. Standard L-shape keys are sold individually and in sets, typically 1.5–10mm metric or 1/16–3/8" imperial. Best for: general workshop use, fasteners requiring accurate torque feel, tight access with the short leg. Limitation: repetitive use is slower and more tiring than T-handle; no angled entry. 2. T-Handle Allen Key A T-handle key has a perpendicular handle bar at the top of the drive shaft, forming a T-shape. The handle gives a comfortable palm grip for fast rotation and significantly more torque than an L-key in normal use. T-handle keys are popular with automotive mechanics and assembly technicians who are driving the same fastener repeatedly throughout a shift — the ergonomic grip reduces fatigue dramatically compared to L-shape use. Many T-handle sets feature a ball-end drive tip, combining the ergonomic handle with the angled-access capability. Ball-end T-handle sets are the preferred choice for engine bay work, bicycle maintenance, and any application involving repetitive fastener driving at moderate torque. Best for: repetitive use, automotive workshop, bicycle maintenance, assembly operations. Limitation: bulkier than L-keys; may not fit in confined spaces where a short L-key shank is needed. 3. Ball-End Allen Key A ball-end key has a rounded ball-shaped tip on the drive end in place of the standard flat hex tip. The ball engagement allows the key to drive a fastener at an angle of up to 25–30 degrees off-axis — useful when a straight approach to the fastener is obstructed by a bracket, housing, or adjacent component. The trade-off is torque capacity. At any angle beyond 0 degrees (straight on), the ball reduces the contact area between the key and the socket. At 25 degrees, the contact area is minimal — applying full torque risks rounding the socket or, for smaller key sizes, snapping the ball off the shank. Ball-end keys are the right tool for positioning fasteners and running them down under low torque. They are not the right tool for final tightening. Always finish with the flat (straight) end for the final seating torque. ⚠️ Ball-end torque limit: Never use the ball end for final tightening — particularly on smaller sizes (under 4mm). The reduced socket engagement concentrates torque on fewer contact points. Under high torque the ball can snap clean off, leaving you with half a key and a partially tightened fastener. Use the straight end for final torque. Best for: running down fasteners where straight access is obstructed, engine bay and machinery work, positioning and alignment tasks. Limitation: not for final tightening; ball-end on sizes under 3mm is fragile under high torque. 4. Folding / Pocket Allen Key Set A folding set houses multiple allen keys on a single pivot — similar in concept to a Swiss Army knife. All the keys fold into the handle body when not in use, making the set compact and portable. Folding sets are popular for bicycle maintenance bags, general DIY kits, and anyone who needs a full size range in a pocket-sized package. The limitation is the pivot mechanism. Folding keys do not lock in the open position on most designs — applying torque puts a bending load on the pivot, which feels imprecise and limits how much force you can safely apply. For occasional light fastener work, folding sets are entirely adequate. For trade use or regular high-torque applications, a proper L-key or T-handle set is more appropriate. Best for: bicycle toolkits, portable DIY kits, light general use, travel and on-site convenience. Limitation: pivot mechanism limits torque; not suitable for tight fasteners or trade use. 5. Hex Bits (for Power and Ratchet Drivers) Hex bits are not allen keys in the traditional sense — they are hexagonal drive bits designed for use in a power driver, cordless drill, or ratchet handle with a bit adapter. They replace a full set of L-keys for applications where you are driving large numbers of hex socket fasteners — assembly operations, furniture manufacturing, or any setting where speed is more important than fine torque feel. Hex bits for hand ratchets and 1/4" drive handles are excellent for workshop use — they give the convenience of a ratchet with hex drive capability, and the ratchet mechanism allows faster work than an L-key in open spaces. Hex bits in power drivers are effective for running fasteners down, but the torque of even a modest cordless drill vastly exceeds the safe torque limit for smaller hex sockets. Use a torque-limited setting when driving hex socket fasteners with power tools, and finish by hand. ⚠️ Impact driver caution: Hex bits under 3mm are at significant risk of shearing under impact driver torque. A standard impact driver produces far more torque than any small hex socket fastener is rated for. Use standard allen keys or a controlled-torque driver for M3 and smaller fasteners. Best for: high-volume assembly, furniture construction, ratchet-drive applications, M6 and larger fasteners. Limitation: no torque feel; risk of socket damage or bit shear on small sizes with power tools. Metric Allen Key Sizes: Complete Chart Metric allen keys are sized by the across-flats dimension of the hexagonal shaft, measured in millimetres. This is the same dimension as the socket in the fastener. Standard metric hex key sets in Australia typically cover 1.5mm through 10mm, with some sets extending to 12mm or 14mm for larger industrial fasteners. The table below shows the standard metric allen key sizes and the ISO metric bolt sizes they correspond to for socket head cap screws (the most common hex socket fastener in industrial applications — see our full SHCS guide for DIN 912 dimensions, grades, and torque values). Note: button head socket screws (ISO 7380) take a hex key one size smaller than the equivalent cap head — for example an M8 button head needs a 5 mm Allen key, not a 6 mm. See our Button Head Socket Screw Guide for the full button-head sizing reference. Allen key size (mm) Matches bolt (ISO metric) Common applications 1.5 mm M2 Precision instruments, electronics, eyewear 2 mm M2.5 Small electronics, camera equipment 2.5 mm M3 Small machinery, bicycle components, 3D printers 3 mm M4 Light machinery, bicycle brakes/derailleurs, electronics enclosures 4 mm M5 General machinery, bicycle cranks and pedals, furniture 4.5 mm M5 (some European) European machinery, some bicycle components — uncommon 5 mm M6 Most common size — automotive, industrial, general engineering 5.5 mm M7 (limited) Some European automotive applications 6 mm M8 Automotive, heavy machinery, structural fasteners 7 mm M10 (some) Industrial equipment, some European machinery 8 mm M10 Heavy industrial, large automotive fasteners 9 mm M12 (some) European industrial equipment, heavy machinery 10 mm M12–M14 Heavy industrial, large socket head cap screws 12 mm M16 Heavy plant, structural connections 14 mm M20 Heavy industrial, large structural applications Most-used metric sizes in Australian workshops: 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm cover the vast majority of general engineering and automotive applications. A standard 9-piece metric set (1.5–10 mm) handles everything from bicycle components to light industrial machinery. ℹ️ Does a 4.5mm allen key exist? Yes — it is a standard ISO size and is included in some extended metric sets. It appears on certain European machinery and some bicycle components. It is not in most standard 9 or 10-piece sets, which is why it often stumps people when they encounter it. If you need one, look for an extended metric set or purchase it individually. Imperial (SAE) Allen Key Sizes: Complete Chart Imperial allen keys are sized in fractions of an inch and follow the ASME B18.3 standard (USA/Canada) or the older Unified Thread Standard. In Australia, imperial hex keys are less common than metric but remain necessary for work on bicycles (particularly US and Japanese-brand drivetrains), older plant and machinery, and any American-branded equipment. Allen key size (inch) Decimal (inch) Approx. metric equivalent Common applications 1/16" 0.0625" ~1.6 mm Precision instruments, small electronics 5/64" 0.0781" ~2 mm Small fasteners, US electronic equipment 3/32" 0.0938" ~2.4 mm Small machinery, some bicycle components 7/64" 0.1094" ~2.8 mm US automotive, some bicycle saddle clamps 1/8" 0.125" ~3.2 mm US machinery, older plant, some bicycle parts 9/64" 0.1406" ~3.6 mm Less common — some US automotive 5/32" 0.1563" ~4 mm US machinery, bicycle stem bolts 3/16" 0.1875" ~4.8 mm US automotive and machinery 7/32" 0.2188" ~5.6 mm US automotive 1/4" 0.250" ~6.4 mm US automotive, older US industrial machinery 5/16" 0.3125" ~7.9 mm Heavy US machinery, older plant 3/8" 0.375" ~9.5 mm Heavy US industrial Metric vs Imperial: Why They Are Not Interchangeable The most expensive allen key mistake in any workshop is using a metric key on an imperial fastener or vice versa. The sizes look similar — a 5mm key looks almost identical to a 3/16" key (4.76mm actual) — but the difference of 0.24mm is enough to reduce full six-point engagement to two- or three-point engagement. The result is rounding of the socket corners, which quickly progresses to a completely stripped drive. The problem is compounded by the fact that a slightly small key can usually be forced in. It feels like it fits. It will turn the fastener — until the torque reaches the point where the key lifts and cams out, taking the socket corners with it. The fastener is now effectively impossible to drive with a hex key and requires extraction. Metric size Actual dimension Closest imperial Imperial actual Gap 4 mm 4.000 mm 5/32" 3.969 mm 0.031 mm — risky 5 mm 5.000 mm 3/16" 4.763 mm 0.237 mm — will strip 6 mm 6.000 mm 1/4" 6.350 mm Too large — won't enter 8 mm 8.000 mm 5/16" 7.938 mm 0.062 mm — very risky ⚠️ How to tell metric from imperial: If the key has no markings, measure across the flats with a digital calliper. A metric key will be a round millimetre number (4.00, 5.00, 6.00). An imperial key will be a fractional inch value (3.969mm for 5/32", 4.763mm for 3/16"). When in doubt, use a calliper — eyeballing the difference between 5mm and 3/16" is not reliable. Ball-End Allen Keys: When to Use Them and When Not To Ball-end keys are genuinely useful tools — in the right application. The ability to drive a fastener at an angle is valuable in confined engine bays, behind panels, and in any situation where a straight approach is impossible. The 25-degree entry angle that a ball-end key allows can turn a 20-minute awkward job into a two-minute one. The limitation is physics: at any angle beyond 0 degrees, the contact area between the ball and the socket decreases. The socket's six flat faces are designed for a flat hex key — the ball contacts them at points rather than across their full face width. This concentrates the applied torque and creates point loading that rounds the socket corners. Practical rules for ball-end use Rule 1 — Use ball-end for access, not torque. Angle the key to access the fastener and run it down. Switch to the straight end for final seating torque. Rule 2 — Maximum 15–20 degrees for any real torque. At 25 degrees the engagement is marginal. Reserve maximum angle for light-torque fasteners only. Rule 3 — Never use ball-end on corroded or tight fasteners. Any fastener that has seized or corroded requires high torque to break free. Ball-end engagement on a seized fastener is a guaranteed socket-stripping scenario. Use the straight end, apply penetrating oil, and give it time. Rule 4 — Size matters. A 2.5mm ball-end key is fragile under any meaningful torque. Treat anything under 3mm as a positioning tool only — no torque beyond finger-tight. Security Hex Keys: Tamper-Resistant Fasteners Standard hex socket fasteners can be driven by anyone with the right allen key — which is why tamper-resistant variants exist for applications where unauthorised removal is a concern. Security hex keys have a small pin or post in the centre of the drive tip that engages a corresponding hole in the fastener head. A standard allen key without the centre pin cannot engage the socket properly. The equivalent system on the Torx side is security Torx (Torx TR / pin-in-Torx) — see our Torx Bit Sizes Guide for the full Torx-family breakdown including security variants. Security hex fasteners are common in: — Public playground equipment and park furniture — Electronic equipment enclosures (consumer electronics, vending machines, ATMs) — Some aftermarket automotive parts — Retail display fixtures — Public infrastructure (bus shelters, signage, lighting) If you encounter a hex socket that a standard allen key will not fully seat in, look closely at the centre of the socket — a small hole indicates a security fastener. Security hex key sets are available separately and are worth keeping in any maintenance toolkit dealing with public or retail environments. Related security drive types you may encounter include Torx (six-pointed star drive, increasingly common in automotive and electronics), Torx Plus (improved engagement version), and clutch drives (figure-eight shape, common on older bus and truck bodywork). Each requires a specific driver type — a standard hex key will not work on these. Which Allen Key Set Should You Buy? The right set depends on your primary application. These recommendations cover the most common AU workshop and trade scenarios. For a general workshop or trade toolbox Start with a 9-piece metric L-key set (1.5–10mm) in chrome vanadium steel. This covers M3 through M12 fasteners and handles the vast majority of Australian machinery, automotive, and general engineering applications. Supplement with a 9-piece imperial set (1/16"–3/8") for work on US-imported equipment, older machinery, and bicycles with American drivetrains. Look for sets where the key sizes are stamped or laser-etched onto each key — unmarked keys are difficult to identify quickly and cause errors. Chrome vanadium (Cr-V) steel is the standard material for professional-grade keys — harder and more wear-resistant than plain carbon steel. For automotive workshop use A ball-end T-handle set in metric (2–10mm) plus a standard L-key set. The T-handle provides ergonomics for repetitive work; the ball-end allows access in confined engine bays. Keep a dedicated straight-end set for final torque. A magnetic holder or rack keeps sizes organised and accessible without rooting through a pouch between uses. For bicycle maintenance Metric is the priority, but imperial appears on some older and US-brand components. A folding set works well in a saddle bag for on-road fixes. For home workshop use, a proper L-key or T-handle set gives better feel for critical fasteners like stem bolts, cleat bolts, and brake caliper mounts — all of which have specific torque requirements and should not be overtightened with a folding set. For light DIY and home use A basic metric L-key set (1.5–8mm) handles furniture assembly, appliance repair, and most household maintenance tasks. Many flat-pack furniture sets include their own basic hex key — these are low-quality and should be replaced with a proper set after the first use. The cheap key that ships with a chair will eventually round out a socket in the furniture itself. Application Recommended set type Metric or imperial General workshop / trade L-shape set, Cr-V steel Both — metric primary Automotive workshop Ball-end T-handle + L-shape Both — metric primary Bicycle maintenance L-shape or T-handle; folding for travel Metric + imperial for older/US bikes Industrial maintenance L-shape Cr-V, extended range to 14mm Both Home DIY Basic L-shape metric set Metric only for most needs Assembly / production Hex bits with ratchet or torque driver Metric 5 Common Allen Key Mistakes 1. Using the wrong size and stripping the socket A key that is even 0.1mm undersized will round off the socket under significant torque. Always confirm the size before applying force. If a key enters the socket but feels slightly loose, stop — find the correct size. A rounded hex socket is often unrecoverable without a socket extractor or fastener drilling. 2. Using imperial on metric (or vice versa) Covered in detail above, but worth repeating: the closest metric and imperial sizes are not close enough. A 5mm key used in a 3/16" socket (4.76mm) will strip it. Keep metric and imperial sets physically separate — different pouches or different sides of a holder — to prevent grabbing the wrong type under pressure. 3. Final tightening with the ball end Ball-end keys are for access and running fasteners down. The straight end is for final torque. Every mechanic who has snapped the ball end off a key did it by forgetting this rule under time pressure. Keep the habit: angle to position, switch to straight to tighten. 4. Using a worn or damaged key Allen keys wear at the drive end. The corners of the hexagonal tip radius over with use, particularly when used at slightly wrong sizes or angles. A worn key that looks fine in the hand will fail to seat fully in the socket — the contact is now on the worn tips rather than the flat faces. Replace keys that show visible rounding at the tip. The cost of a new key is trivial versus the cost of extracting a stripped fastener. 5. Using hex bits with an impact driver on small fasteners An impact driver is not a torque-controlled tool. Even on a low setting, the impulse torque of an impact driver will exceed the safe drive torque for M4 and smaller hex socket fasteners. Use a proper allen key or a controlled-torque screwdriver for small fasteners. Reserve hex bits in an impact driver for M6 and larger, and use the torque limiter setting where available. AIMS Industrial stocks a full range of allen key sets and hex keys in metric and imperial for workshop and industrial applications. Browse the hand tools range for current stock. For related spanner and socket selection guidance, see our guides on types of spanners and drill bit types. Frequently Asked Questions What is the difference between an Allen key and a hex key? There is no functional difference — they are the same tool described by different names. "Allen key" is the term used in Australia and the UK, derived from the Allen Manufacturing Company trademark that became generic. "Hex key" is the technically correct term based on the tool's hexagonal cross-section and is used in engineering standards and trade catalogues. "Allen wrench" is the North American equivalent. All three terms describe the same L-shaped hexagonal steel driver. What are the standard metric Allen key sizes? Standard metric sets in Australia typically cover 1.5 mm, 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm — a 9-piece set. Some sets extend to 12 mm and 14 mm for larger industrial fasteners. The most commonly needed sizes in general Australian workshop use are 2.5 mm (M3), 3 mm (M4), 4 mm (M5), 5 mm (M6), 6 mm (M8), 8 mm (M10), and 10 mm (M12). Does a 4.5mm Allen key exist? Yes, 4.5 mm is a standard ISO metric size. It is not included in most standard 9 or 10-piece metric sets, which is why it catches people by surprise. It appears on some European machinery and certain bicycle components. If you need a 4.5 mm key, look for an extended metric set (which typically runs 1.5–12 mm and includes 4.5 mm) or purchase it as a single key. Is there a 9mm Allen key? Yes, 9 mm is a standard ISO metric size. Like 4.5 mm, it is not in most standard 9-piece sets — which stop at 8 mm or 10 mm and skip 9 mm. It is used on some M12 fasteners with non-standard socket dimensions and on some European industrial and automotive equipment. Extended metric sets that run to 12 mm or 14 mm include 9 mm. Can I use an imperial Allen key on a metric bolt? No — and doing so will strip the socket. Imperial and metric sizes appear similar but are not identical. The closest pairs (such as 5mm metric and 3/16" imperial, which is 4.76mm) differ by enough to reduce full six-point engagement to partial contact on two or three points. Under torque, the key cams out and rounds the socket corners. Always match the key to the fastener's standard — metric to metric, imperial to imperial. What Allen key size do I need for an M6 bolt? An M6 ISO metric socket head cap screw uses a 5 mm Allen key. This is one of the most common combinations in Australian engineering and automotive applications. For reference: M3 = 2.5 mm, M4 = 3 mm, M5 = 4 mm, M6 = 5 mm, M8 = 6 mm, M10 = 8 mm, M12 = 10 mm. What is a ball-end Allen key used for? A ball-end Allen key allows the tool to drive a fastener at an angle of up to 25–30 degrees off-axis — useful when a direct straight approach is blocked by a housing, bracket, or adjacent component. They are commonly used in engine bays, behind panels, and in any application with restricted access. The ball provides positioning and run-down capability, not final torque — always use the straight end for final tightening. Can you use a ball-end Allen key for final tightening? No. The ball end reduces contact area between the key and the socket, particularly at any angle. Using a ball end for final torque risks rounding the socket corners, and on smaller sizes (under 4 mm) can snap the ball off the key shank. Use the ball end to access and run down the fastener, then switch to the straight end for final seating torque. This is the most commonly ignored rule in ball-end key use. What is the difference between a T-handle and L-shape Allen key? An L-shape key is the standard two-leg bent-bar configuration — one leg drives, the other is the handle. A T-handle key has a perpendicular bar at the top forming a T-shape, providing a palm grip for faster rotation and greater ergonomic comfort during repetitive use. T-handle keys are faster and less fatiguing for high-volume work. L-shape keys give better torque feel and fit into tighter spaces with the short leg. For fine torque-sensitive fasteners, the direct feedback of an L-key is preferred over a T-handle. What is a security hex key? A security hex key (also called a tamper-proof hex key or pin-in-hex key) has a small centre pin or post at the tip that engages a corresponding hole in the fastener head. A standard allen key cannot fully seat in a security hex socket — the centre hole prevents it from engaging properly. Security hex fasteners are used on playground equipment, electronic enclosures, public fixtures, and retail fittings to prevent unauthorised removal. Security hex key sets are available separately and should be in any maintenance kit dealing with public infrastructure or electronic equipment. Why does my Allen key keep slipping? Slipping almost always means the key is undersized for the socket. Either you have the wrong size, you are using an imperial key on a metric fastener (or vice versa), or the key is worn and the tip corners have rounded off. Check the size match first — confirm with a calliper if unsure. If the key is correct but worn, replace it. A slipping key that is allowed to continue will strip the socket, turning a simple job into a fastener extraction problem. What Allen key set should I buy for a general workshop? For a general Australian workshop, start with a 9-piece metric L-key set in chrome vanadium (Cr-V) steel covering 1.5–10 mm. Add a 9 or 10-piece imperial set for work on US-imported equipment and bicycles. Look for sets with sizes etched onto each key and a secure holder or pouch — loose keys in a drawer guarantee you will spend five minutes finding the right size every time. For automotive or trade use, add a ball-end T-handle metric set for access and repetitive work. For metric and imperial spanner cross-references (M3-M30, AF sizes), see our Spanner Size Chart. People Also Ask — Allen Keys Q: What is the difference between an allen key, a hex key and an allen wrench? Allen key, hex key, and allen wrench all refer to the same tool — an L-shaped bar of hexagonal cross-section steel used to drive fasteners with a hexagonal socket. 'Allen key' and 'allen wrench' are trade name-derived terms; 'hex key' is the generic technical name. In Australian trade use, 'allen key' is the dominant term; engineering and tooling catalogues often use 'hex key'. They are the same tool regardless of the name used. Q: Are metric and imperial allen keys interchangeable? No — metric and imperial allen keys are not interchangeable, even when the sizes appear very close. Metric keys are sized in millimetres (such as 3 mm, 4 mm, 5 mm, 6 mm) while imperial keys are sized in fractional or decimal inches (such as 5/32", 3/16", 1/4"). Although some sizes are very close — for instance, 5 mm and 13/64" differ by only 0.05 mm — using the wrong size will cause rounding of the socket or key, making subsequent tightening and removal increasingly difficult. Always match the key to the fastener's specification. Q: When should I use a ball-end allen key versus a standard flat-end key? A ball-end allen key allows you to engage the fastener at angles of up to approximately 25–30° off-axis — useful when working in confined spaces where a straight approach is not possible. However, ball-end engagement transmits less torque than a flat-end key and can round out the socket if used to apply high torque, particularly on fasteners that are tight or corroded. Use the ball end for initial engagement and light adjustment only; switch to the standard flat end for final tightening or for breaking loose a tight fastener. Q: What allen key sizes are most commonly needed for industrial and trade work? For general workshop and trade work in Australia, the most frequently needed metric allen key sizes are 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm — these cover the majority of socket head cap screws, grub screws, and button head screws found on machinery, vehicles, and equipment. A complete metric set from 1.5 mm to 10 mm (or 12 mm) covers almost all general requirements, with the 4 mm, 5 mm, and 6 mm sizes being by far the most used.
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