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.

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

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?"

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.