Product Guides
Stripped Thread Repair Guide: Helicoil, Recoil & Inserts
What Is a Stripped Thread? A stripped thread is a threaded hole — or external thread — where the thread profile has been damaged to the point that the original fastener no longer engages reliably. The thread crests have been crushed, sheared, or pulled out; the helical groove that should grip the bolt is now smooth or partially intact at best. The bolt either spins freely without grabbing, pulls out under hand pressure, or strips deeper as you try to tighten it. The joint cannot develop clamping force. Stripped threads happen for predictable reasons: Over-torquing — applying torque beyond the parent thread's yield point, particularly in soft parent materials (aluminium, magnesium, plastic). The most common cause across AU automotive and industrial work. Cross-threading — starting the bolt at an angle and forcing it. Damages the lead thread and propagates as the bolt is tightened. Repeated cycling on a soft parent — aluminium engine blocks with spark plug threads removed and reinstalled hundreds of times eventually wear out the parent thread. Corrosion damage — outdoor and marine threads where the parent metal corrodes and the thread profile degrades. Wrong-size fastener — the wrong thread pitch or diameter forced into a hole. Heat damage — repeated thermal cycling or localised overheating annealing the parent material. Thread repair is appropriate when the parent component is expensive or impractical to replace — engine blocks, gearbox housings, machine castings, marine outboard blocks, structural plate. It is not always the right answer; sometimes drilling the hole oversize and using a larger bolt, or replacing the parent component entirely, is faster and cheaper. This guide covers when to repair, what to use, and how to do it. The full AIMS thread repair range — Recoil wire inserts and keyserts (the AU-stocked brand), Champion budget kits, and individual taps and inserts — is at the Recoil collection at AIMS. Recoil — The Australian Thread Insert Brand Recoil is the AU-founded thread insert brand stocked at AIMS Industrial. The Recoil product range covers the two main thread insert technologies in industrial supply: Recoil wire inserts (helical inserts) — the diamond-cross-section stainless wire wound into a helical coil that screws into a tapped oversize hole. Dimensionally compatible with Helicoil. The general-purpose option for most AU repair work. Recoil Keyserts (key-locking inserts) — solid threaded bushings with locking keys driven into the parent material. Mechanically locked into the parent thread, used where vibration resistance and fail-proof installation are critical. Recoil's Australian heritage is worth knowing. The Recoil brand originated in Australia and remains the dominant AU industrial thread insert brand at AIMS and through specialist tool suppliers. The Recoil product line is dimensionally compatible with international Helicoil and Heli-Coil products at most sizes — the inserts, taps, and installation tools interchange across most metric and imperial threads. For most AU thread repair work in this guide we will refer to Recoil and Helicoil together where they are functionally interchangeable, and call out the specific differences where they matter. If you are working off an older purchase order or service manual, our Recoil 2007 → 2013 → 2023 part number cross-reference translates legacy codes to current RC kit numbers. Recoil Wire Inserts — How They Work and When to Use The wire insert — Recoil's flagship product, equivalent to Helicoil and Heli-Coil — is the most widely used thread repair technology globally. It is supplied as a tightly-wound stainless steel coil with a diamond cross-section. Each turn of the coil forms a thread profile when installed in a properly tapped oversize hole. How the wire insert installs The damaged threaded hole is drilled out to the insert's specific tap drill size, then tapped using a special oversize tap (the Recoil/Helicoil tap is larger than a standard tap of the same nominal thread because it cuts the thread that will receive the insert). The insert is wound into the new tapped thread using a dedicated installation tool. The diamond cross-section springs into the parent thread under tension, locking the coil in place. The driving tang at the bottom of the coil is then snapped off using a punch and the tang break-off tool — the bolt cannot enter the insert until the tang is removed. The repaired hole now accepts the original-size bolt as if the parent thread had never been damaged. Why wire inserts are stronger than the original thread A counterintuitive engineering point. A properly installed wire insert distributes clamping load across the wire's full coil contact with the parent thread — significantly more bearing area than the original tapped thread provided. The wire's spring action also accommodates minor parent thread imperfections that would have weakened a standard thread. A correctly-installed Recoil or Helicoil insert is mechanically stronger than the original thread, not just equivalent. This is why thread inserts are used on aluminium aerospace components and engine blocks where the OE thread design is the weak link. When to choose wire inserts General thread repair on engine blocks, machine castings, gearbox housings Aluminium parent material where the soft thread strips repeatedly Manifold studs, head studs, mounting points Cost-sensitive repairs where high-volume insertion is needed Threads that will not be cycled often (assembly threads rather than service threads) Recoil Keyserts — Key-Locking Inserts for Vibration-Critical Applications The Recoil Keysert (also called a key-locking insert or Keensert in US trade language) is a solid threaded bushing — not a wound coil. The Keysert has external threads on the body that screw into a tapped oversize hole, with locking keys (typically four small keys around the perimeter) that are driven down into the parent material once the bushing is fully installed. The locking keys mechanically prevent the insert from rotating, even under vibration. How Keyserts differ from wire inserts Feature Recoil wire insert (Helicoil) Recoil Keysert (key-locking) Construction Wound stainless wire coil Solid threaded bushing with locking keys Locking mechanism Spring tension against parent thread Mechanical keys driven into parent material Vibration resistance Good Excellent — fail-proof Removal Possible (drill out tang then unscrew) Difficult — must drill out the locking keys Wall thickness required in parent Less material needed More parent material needed for keys Cost per insert Lower Higher Best for General repair, soft parents, engine blocks Aerospace, vibration-critical, fail-proof joints Recoil Keyserts are specified in aerospace, defence, motorsport, and any application where insert rotation-loosening would be catastrophic. The mechanical keys make the insert genuinely permanent — drilling the keys out is the only removal method, which is itself an installation reliability indicator. When to choose Keyserts Aerospace and defence applications where fail-proof matters Motorsport and high-vibration machinery Any joint where insert rotation under vibration would cause catastrophic failure Critical structural mounting points Where the parent material is sufficient to accept the locking keys TimeSert — The Solid Bushing Alternative TimeSert is a different thread repair technology — a solid one-piece threaded bushing manufactured to a specific bolt size. Unlike a wire insert, TimeSert installs as a single rigid component. The defining feature is the flared top: a small lip at the top of the bushing sits in a counterbore prepared in the parent material, physically preventing the insert from being driven too deep — and critically, preventing it from dropping into engine cylinders or other internal cavities. TimeSert installation requires: Drilling the parent hole to TimeSert's specific drill size (smaller than a Helicoil/Recoil tap drill — TimeSert needs less material removed) Counterboring the top of the hole to accept the flared head Tapping the hole to the TimeSert thread spec Threading the TimeSert in until the flare seats in the counterbore Using TimeSert's installation tool to cold-roll-expand the bottom of the bushing — this locks the insert into the parent thread by cold deformation The cold-roll bottom expansion is what locks the TimeSert in place. There is no tang to break off, no spring tension, no locking keys — just a permanently expanded bottom that grips the parent thread mechanically. When to choose TimeSert Spark plug threads — the AU automotive standard. Spark plug threads cycle every service interval; the rigid TimeSert handles repeated removal and reinstallation better than a wire insert. Drain plugs and oil bolt holes — service threads removed and reinstalled regularly Engine cylinder threads where insert drop-in is unacceptable — TimeSert's flare prevents the insert from falling into the cylinder during installation. This is the safety reason TimeSert dominates aluminium head spark plug repair. Cover bolt threads — covers that come off and back on multiple times in service The trade-off is cost — TimeSert kits cost considerably more than Recoil/Helicoil kits, and TimeSert requires its specific tooling for each thread size (no interchange with Helicoil tools). For one-off repairs where the application doesn't strictly need TimeSert, Recoil/Helicoil is the cost-effective choice. Helicoil vs Recoil — Same Product, Different Brand This is the disambiguation most AU industrial buyers don't realise they need. Helicoil and Recoil are essentially the same product — wire thread inserts to similar dimensional standards — manufactured by different companies. The terms are used interchangeably in AU trade language much as "Biro" became the generic term for ballpoint pens in Australia. Aspect Helicoil Recoil Origin US (Heli-Coil Corporation, now Stanley Black & Decker) AU heritage, now part of Stanley Black & Decker Wire insert dimensions Industry standard helical wire Industry standard helical wire — interchangeable Tap drill sizes Same as Recoil Same as Helicoil Tap dimensions Special oversize tap, brand-specific Special oversize tap, brand-specific Installation tool Brand-specific tool Brand-specific tool — but works with Helicoil inserts AU stock at AIMS Not the primary brand Primary brand — AU stocking advantage For AU buyers: when a Helicoil is specified on an OE workshop manual or a parts catalogue, a Recoil insert of the same nominal size will fit and perform identically. The exceptions are the installation tap and the installation tool — these are brand-specific and not interchangeable. If you have a Helicoil kit's tools, use Helicoil inserts; if you have a Recoil kit's tools, use Recoil inserts. Steel vs Stainless Inserts — Interchangeability and Galvanic Corrosion Recoil and Helicoil inserts are stocked in two main material grades: stainless steel (304 or 316) and carbon steel (typically phosphor bronze or coated steel for some applications). The question that comes up regularly: can you mix stainless inserts with steel bolts in steel parents, or vice versa? The short answer: generally yes for dry indoor and most ambient applications, but mixing materials in wet, salt-laden, or chemical environments creates galvanic corrosion risk. The mechanical question Insert material and bolt material do not mechanically need to match. The insert provides the thread; the bolt is the fastener. The joint's clamping load is determined by the bolt grade (e.g. Class 8.8 or 12.9), not by the insert material. A stainless insert with a Class 12.9 carbon steel bolt achieves the bolt's full clamping capacity provided the insert and parent thread are correctly sized. The corrosion question Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (water, particularly salt water). The less noble metal corrodes preferentially. The combinations that matter for thread inserts: Insert Bolt Parent material Indoor / dry use Wet / coastal / marine use Stainless Stainless Stainless ✓ Fully matched ✓ Specify 316 in marine Stainless Carbon steel Stainless or steel ✓ Generally OK ⚠️ Carbon steel bolt corrodes preferentially Stainless Stainless Aluminium ✓ Generally OK ⚠️ Aluminium parent corrodes preferentially in salt Carbon steel Carbon steel Aluminium ✓ Generally OK ⚠️ Aluminium parent corrodes; use anti-seize Carbon steel Stainless Any ✓ Generally OK ⚠️ Carbon steel insert corrodes preferentially Practical AU rule: For indoor industrial, dry environments, and general workshop repair — interchange freely between stainless and carbon steel inserts and bolts. For coastal Australian sites within 1 km of the surf, marine applications, swimming pool fittings, food processing brines, and chemical environments — match all three components (insert, bolt, parent) to the same material family or specify all stainless 316. Use anti-seize compound on threads to slow any galvanic action where mixed materials are unavoidable. Step-by-Step Thread Repair with Recoil/Helicoil The four-step procedure works across all wire-insert systems (Recoil, Helicoil, Heli-Coil, KATO). Specific tap drill sizes and tap dimensions vary by brand and insert size — refer to the kit instructions. Step 1 — Drill the damaged thread oversize Use the drill bit supplied with the kit (or specified in the brand's drill chart). The drill removes the existing damaged thread and creates a clean cylindrical hole sized to accept the special oversize tap. Drill straight — perpendicularity matters. Apply cutting oil. Use a drill press or a guide where accuracy is critical. Step 2 — Tap the hole with the kit's special tap The kit-supplied tap is larger than a standard tap of the nominal bolt size. It is dimensioned specifically to cut the thread that will receive the insert. Apply cutting fluid liberally. Turn the tap clockwise to cut, then back off a quarter turn to break the chip — repeat throughout the cut. The quarter-turn back-off is non-negotiable; skip it and the tap will bind, the chip will jam, and the tap will break (sending you to the broken tap removal procedure). Continue until the tap has cut a full thread through the hole depth. Remove the tap, clear chips from the hole. Step 3 — Install the insert Load the insert onto the installation tool with the tang at the bottom. Wind the insert into the tapped hole, applying light downward pressure. Continue winding until the top of the insert is approximately 1/4 to 1/2 turn below the top surface of the parent material. This below-flush position is intentional and correct — the insert is not supposed to be flush with the surface. Reverse the installation tool to release torque. The insert expands slightly to lock against the new parent thread. Step 4 — Break off the tang Use the kit's tang break-off punch (a simple cylindrical punch). Insert the punch into the installed insert until it contacts the tang. Strike the punch sharply with a hammer. The tang shears off cleanly at the notched break point. Remove the broken tang from the hole. The repaired hole now accepts the original bolt size. Test fit the bolt to confirm the thread is clean and engaging properly. Practical buying tip: Budget for 25-50% extra inserts on any repair job. Some inserts will break or distort during installation, particularly if the tapped hole has minor imperfections or the installation tool is worn. Cheap kits' installation tools are the most common cause of insert damage during install — invest in a quality tool. Insert Size Selection — Drill, Tap and Insert Reference Recoil and Helicoil insert sizing follows a consistent pattern: the insert designation matches the original bolt size (e.g. M8 insert for M8 bolt repair), but the drill and tap are oversize to the original bolt thread. Bolt size Insert designation Drill size (mm) Tap (special) Insert lengths typically stocked M3 M3 insert 3.3 M3 STI tap 1.5d, 2d M4 M4 insert 4.3 M4 STI tap 1.5d, 2d M5 M5 insert 5.5 M5 STI tap 1.5d, 2d, 2.5d M6 M6 insert 6.3 M6 STI tap 1.5d, 2d, 2.5d, 3d M8 M8 insert 8.4 M8 STI tap 1.5d, 2d, 2.5d, 3d M10 M10 insert 10.4 M10 STI tap 1.5d, 2d, 2.5d, 3d M12 M12 insert 12.4 M12 STI tap 1.5d, 2d, 2.5d, 3d M14 M14 insert 14.5 M14 STI tap 1.5d, 2d, 3d M16 M16 insert 16.5 M16 STI tap 1.5d, 2d, 3d M20 M20 insert 20.5 M20 STI tap 1.5d, 2d, 3d M24 M24 insert 24.5 M24 STI tap 1.5d, 2d, 3d Insert length is given in multiples of the bolt diameter (d). 1.5d is the standard length for most general repair work; 2d and 2.5d are used where higher clamping load or extra thread engagement is needed; 3d is used for high-load critical applications, particularly in soft parent materials. For the matching tap selection, see our Tap & Die Guide — note that thread insert taps (STI taps) are different from standard taps and are not interchangeable with a standard tap & die set. Common Australian Applications Engine block thread repair The most common AU thread repair application. Aluminium head spark plug threads stripped from over-torquing or thread wear → TimeSert (anti-drop flare design preferred for cylinders). Engine block manifold studs, head bolts, and accessory mounts → Recoil/Helicoil (cost-effective, sufficient for assembly threads). Particularly common on motorcycles, older vehicles, and equipment with aluminium heads. Marine outboard motor repair Salt water corrosion damages aluminium outboard motor block threads — common on Mercury, Yamaha, Honda outboards. Stainless 316 inserts with stainless 316 bolts is the standard; carbon steel inserts will corrode and seize. Use anti-seize on installation. The exhaust manifold and cooling water gallery threads are the highest-frequency repair points. Industrial machinery and pump housings Cast iron pump bodies, machine castings, and gearbox housings with stripped threaded mounting holes. Recoil wire inserts handle the bulk of this work; Keyserts where vibration is a concern. Motorcycle and small-engine repair Aluminium crankcase covers, drain plugs, valve cover bolts, sprocket cover bolts. AU motorcycle workshops use Recoil/Helicoil for most repairs; TimeSert for spark plug threads where they cycle frequently. Agricultural and 4WD off-road Tractor PTO covers, implement mounting threads, differential cover bolts, hub stud threads. Cast iron and steel parents — Recoil wire inserts are the standard, with Keyserts for vibration-critical mountings. Aerospace and high-reliability applications Recoil Keyserts (key-locking inserts) — the aerospace standard. Used in airframe components, defence equipment, motorsport, and any application where insert rotation under vibration would cause catastrophic failure. When NOT to Use a Thread Insert — and the Loctite/JB Weld Debunk Drill out and use a larger bolt If the application allows a larger bolt size, drilling the damaged hole oversize and re-tapping to the next thread size (e.g. M8 stripped → drill out to M10) is faster, cheaper, and equally reliable. Common where the design is not size-specific and the bolt circle clearance allows. Saves the cost of a thread insert kit and the installation time. Replace the parent component Where the parent component is cheap or readily available, replacement is sometimes faster than repair. A stripped bolt hole in a $50 cover plate is not worth a $200 thread repair kit. Make the economic call: cost of repair (kit + labour + risk) vs cost of replacement. Loctite, JB Weld and "thread filler" — the debunk Loctite and JB Weld will NOT structurally repair a stripped thread. Loctite is a thread retaining adhesive designed to prevent vibration loosening on a sound thread — it has no structural strength to rebuild missing thread material. JB Weld and similar epoxies will fill a stripped hole and bond to the parent material, but the resulting joint is weaker than the original thread by an order of magnitude — entirely inadequate for any load-bearing or service-removable application. These products are useful for dust-tight cover bolts, plastic threads, and similar non-structural applications. They are not a substitute for a proper thread repair on any joint that needs to develop clamping load. If a forum or YouTube video suggests "just glue it" — that is appropriate only for non-structural applications. For any joint that will see vibration, load, or service removal, install a Recoil or TimeSert insert. The repair is permanent and reliable; the glue is a temporary fix that will fail. AIMS Industrial Thread Repair Range The full AIMS thread repair stock — Recoil inserts, Recoil tools, Champion budget kits, individual taps — is at the Recoil collection at AIMS. Recoil — the AU primary brand The Recoil range stocked at AIMS covers: Recoil wire inserts — stainless steel, M3 through M24 metric, 1.5d / 2d / 2.5d / 3d lengths, in individual packs and kit form Recoil Keyserts — key-locking inserts for vibration-critical applications, M5 through M16 Recoil installation tools — kit-specific installation tools, taps, drills, and tang break-off punches Recoil thread repair kits — complete thread repair sets in common sizes (M5 / M6 / M8 / M10 / M12) Champion — the budget alternative For occasional repair work and non-critical applications, the Champion CTRK14125 Thread Repair Stainless Steel Kit is a cost-effective option. The kit covers common sizes for general workshop repair. Budget Champion kits are appropriate for one-off jobs, hobby workshops, and non-critical applications. For serious workshop work with regular thread repair, the Recoil range is the better long-term investment. Companion product groups Stud Extractor Guide (Art 138) — when removing the broken fastener that damaged the thread Broken Tap Removal (Art 30) — when the tap breaks during the repair installation Tap & Die Guide (Art 41) — note that thread insert taps are different from standard taps Penetrating Oil Guide (Art 67) — for removing the original damaged fastener Thread Locking & Sealing Guide (Art 44) — Loctite has its place, but not for thread repair Bolt Grade Chart (Art 11) — matching bolt strength to repaired joint Frequently Asked Questions What is a stripped thread? A stripped thread is a threaded hole or external thread where the thread profile has been damaged so that the original fastener no longer engages reliably. The thread crests have been crushed, sheared, or pulled out, leaving a smooth or partially-intact surface that cannot develop clamping load. Common causes include over-torquing (especially in aluminium parent material), cross-threading, repeated cycling, corrosion damage, wrong-size fastener, and heat damage. Repair using a thread insert (Recoil, Helicoil, TimeSert) restores the original thread size in the damaged hole. What is the difference between Helicoil and Recoil? Helicoil and Recoil are essentially the same product — wire thread inserts to similar dimensional standards — manufactured by different companies (both now part of Stanley Black & Decker). The wire inserts themselves interchange dimensionally for most metric and imperial sizes. The exception is the installation tap and the installation tool — these are brand-specific. If you have a Helicoil kit's tools, use Helicoil inserts; if you have a Recoil kit's tools, use Recoil inserts. Recoil is the AU-founded brand and the primary stock at AIMS Industrial. How do you repair a stripped thread? The standard wire-insert repair procedure is: (1) drill the damaged hole oversize using the drill bit supplied with the thread repair kit; (2) tap the hole with the kit's special oversize tap (different from a standard tap); (3) wind the insert into the tapped hole using the installation tool until the insert sits 1/4 to 1/2 turn below the surface; (4) break off the driving tang at the bottom of the insert using the kit's punch. The repaired hole then accepts the original-size bolt as if the parent thread had never been damaged. For premium / high-cycle applications, a TimeSert solid bushing is installed similarly but with a counterbore and cold-roll-expansion finish. What is the difference between Helicoil and TimeSert? Helicoil (and Recoil) are wire inserts — a coiled diamond-cross-section wire that springs into place. TimeSert is a solid one-piece threaded bushing with a flared head that sits in a counterbore and a cold-rolled bottom that expands during installation. Wire inserts are cheaper, more widely stocked, and suitable for general repair. TimeSert costs more but tolerates repeated removal and reinstallation better, and the flared head physically prevents the insert from dropping into engine cylinders during installation. Use Helicoil/Recoil for assembly threads and one-off repair; use TimeSert for spark plug threads, drain plugs, and any thread that will be cycled frequently in service. Are thread inserts as strong as the original thread? Properly installed wire thread inserts are typically stronger than the original thread, not just equivalent. The wire insert distributes clamping load across the wire's full coil contact with the parent thread — significantly more bearing area than the original tapped thread provided. The wire's spring action also accommodates minor parent thread imperfections. This is why thread inserts are used as original equipment in aluminium aerospace components and aluminium engine blocks where the OE thread design is the weak link. Improper installation (insert too high, tang not removed, wrong tap drill size) is the only common reason inserts fail. Will Loctite fix a stripped thread? No. Loctite is a thread retaining adhesive designed to prevent vibration loosening on a sound thread — it has no structural strength to rebuild missing thread material. For non-structural cosmetic applications (dust covers, plastic threads, decorative bolts) Loctite may temporarily hold a stripped fastener, but for any joint that develops clamping load — engine bolts, structural fastenings, anything load-bearing — Loctite is not a thread repair. Install a Recoil, Helicoil, or TimeSert insert; the repair is permanent and reliable. Will JB Weld fix a stripped thread? No. JB Weld and similar epoxies will fill a stripped hole and bond to the parent material, but the resulting joint is weaker than the original thread by an order of magnitude — entirely inadequate for any load-bearing or service-removable application. Some YouTube tutorials and forum posts suggest using JB Weld for thread repair; this advice is appropriate only for non-structural plastic-cover bolts or decorative fastenings. For any structural or service thread, install a proper thread insert. What size drill bit do I need for an M8 Recoil insert? An M8 Recoil insert requires an 8.4 mm drill bit (some kits specify 8.5 mm — refer to your specific kit's instructions). This is larger than a standard M8 tap drill (6.8 mm) because the Recoil/Helicoil tap must cut a larger thread to receive the insert. The drill, special tap, and installation tool are all matched to the insert size and must be used together. Thread repair kits supply all three components — never substitute a standard M8 tap for the special insert tap; the threads will not match and the insert will not seat correctly. Can you reuse a thread insert? Wire inserts (Recoil, Helicoil) are not designed for reuse — once removed, the spring tension is lost and the insert no longer locks reliably. Replace any insert that has been removed. TimeSert solid bushings can be reused if removed carefully (the cold-roll bottom expansion does not reset to its installed dimension), but in practice replacement is the standard. Keyserts cannot be reused — the locking keys are deformed during installation and removal requires drilling them out, which destroys the insert. How do you remove a Helicoil or Recoil insert? Wire insert removal requires a Helicoil/Recoil extraction tool — a small tapered tool that bites into the top of the coil and unscrews it counterclockwise. If the original tang has been removed (as it should be after installation), the extraction tool grips the coil's top turn. If the insert is stuck or damaged, the removal procedure is to drill out the insert with a drill bit slightly smaller than the parent thread's tap drill — this destroys the insert but preserves the tapped hole, allowing a new insert to be installed. What is a Keysert and when do you use one? A Recoil Keysert (also called a key-locking insert or Keensert) is a solid threaded bushing with locking keys that are driven into the parent material after the bushing is installed. The mechanical keys prevent the insert from rotating under vibration — a fail-proof installation. Used in aerospace, defence, motorsport, and any vibration-critical application where wire insert rotation-loosening would cause catastrophic failure. Trade-offs: higher cost than wire inserts, more parent material required to accept the locking keys, removal requires drilling out the keys. For general repair, Recoil wire inserts are the cost-effective choice; for fail-proof critical applications, specify Keyserts. Can I just drill out the hole and use a larger bolt? Often yes. If the application allows a larger bolt size (the bolt circle clearance permits, the design is not size-specific, and the parent material is thick enough), drilling the damaged hole oversize and re-tapping to the next thread size (M8 → M10, M10 → M12) is faster, cheaper, and equally reliable. Saves the cost of a thread insert kit and the installation time. The decision factors: is the bolt size constrained by the design (mating component, OE specification, hole pattern), and is the parent material thick enough to accept a larger thread? If both are yes, drilling oversize is often the better answer. Can I mix steel and stainless inserts with different bolt materials? Mechanically yes — the insert provides the thread; the bolt is the fastener; clamping load is determined by bolt grade not insert material. For dry indoor and most ambient industrial applications, mixing stainless inserts with carbon steel bolts (or vice versa) is acceptable. The caveat is galvanic corrosion in wet, salt-laden, or chemical environments. In coastal AU sites within 1 km of surf, marine, swimming pool, food processing brine, and chemical environments, match all components (insert, bolt, parent) to the same material family or specify all stainless 316. Use anti-seize compound on threads to slow galvanic action where mixed materials are unavoidable. What's the best thread repair for engine blocks? Depends on the specific thread. For aluminium head spark plug threads (cycling every service interval, in cylinder so insert drop-in matters), TimeSert is the AU automotive standard — the flared head prevents the insert dropping into the cylinder during installation. For engine block manifold studs, head bolts, accessory mounts, and other assembly threads (installed once, rarely removed), Recoil/Helicoil wire inserts are the cost-effective choice. Marine outboard motor blocks (salt corrosion on aluminium) need stainless 316 inserts with stainless 316 bolts. Match the insert technology to the application's cycling and environmental demands. How tight should I install a thread insert? The insert itself does not have a specified torque — installation is done by hand using the kit's installation tool, winding the insert into the tapped hole until the top of the insert sits 1/4 to 1/2 turn below the parent surface. This below-flush position is intentional and correct. The bolt that is then installed into the repaired hole is torqued to the original bolt's specification — the insert does not change the bolt torque value. As a guide for AU automotive: M6 ≈ 8-10 Nm, M8 ≈ 20-25 Nm, M10 ≈ 40-50 Nm, M12 ≈ 65-80 Nm — always defer to the OE workshop manual where one is specified. Apply anti-seize on stainless threads before installing the bolt. Pair this with our Metric Bolt Size Guide for the thread pitch, AF dimension and grade options at every common size. Share: Share on Facebook Share on X Pin on Pinterest Previous Post Stud Extractor Guide: Cam-Grip Tools, Broken Stud Removal & When to Use Each Type Next Post Taper Lock Bush Guide People Also Ask — Stripped Thread Repair Q: What causes threads to strip and how can it be prevented? Thread stripping occurs when the clamping force generated by tightening exceeds the shear strength of the thread material, or when a fastener is over-torqued, cross-threaded during assembly or the thread is corroded and seized. Soft parent materials such as aluminium and cast iron are particularly vulnerable. Prevention includes using the correct torque specification, ensuring fasteners are started straight, using thread lubricant on corrosion-prone assemblies, and choosing the right thread form and fit class for the application. Where repeated assembly is required in soft materials, installing a thread insert during initial manufacture is the best preventive measure. Q: What is the difference between a Helicoil insert and a solid thread insert? A Helicoil insert is a coiled stainless steel wire insert that is screwed into an oversized tapped hole to provide a new internal thread matching the original thread size. It is flexible and locks into the parent material under load. A solid insert (such as a Keensert or E-Z Lok type) is a solid piece of harder material — typically stainless steel or bronze — that is pressed or threaded into the parent material and provides a rigid, stronger thread form. Solid inserts are generally stronger and better suited to high-load or impact applications; wire inserts are more forgiving of slight misalignment and are widely available for common thread sizes. Q: Can I repair stripped threads in aluminium without removing the component? Yes — in many cases, thread inserts can be installed in aluminium components without removal. Drill the stripped hole to the insert tap drill size, tap the new larger thread, and screw in the insert. This can be done in situ as long as there is access to drill and tap in alignment with the original thread axis. Misalignment during drilling is the main risk of in-situ repair — a drill guide or bushing helps keep the repair concentric. For critical threaded joints in load-bearing aluminium structures, always consult a structural engineer before relying on a field repair. Q: When should I use a thread repair kit versus replacing the component? Thread repair using an insert is appropriate when the parent component is expensive, difficult to obtain or difficult to remove, and when the repair can restore thread strength equal to or better than the original. Replace the component when the stripped thread is in a safety-critical location and the repair cannot be verified, when multiple threads are damaged or the parent material is cracked, or when the component is inexpensive and easy to replace. For mass-produced fastener threads in non-critical locations — such as an engine oil drain plug thread — a time-sert or Helicoil repair is a well-established and accepted repair method. Q: What is the best way to remove a bolt that has seized in a stripped thread? For a bolt seized into a stripped thread, apply penetrating fluid and allow time for it to work into the joint before attempting to remove. Heat from a heat gun or torch (where safe) expands the parent material and can break the corrosion bond. If the bolt head is accessible, try a larger torque with a breaker bar before using impact tools, which can worsen the damage. If the bolt head is damaged, use a bolt extractor, weld a nut to the stub, or carefully drill out the centre of the bolt and use an extractor bit. Drilling out a seized bolt is a last resort but is often the fastest way to clear a badly corroded assembly. 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Nyloc Nut Guide: DIN 985, Sizes, Temperature Limits & When to Use Self-Locking Nuts
What Is a Nyloc Nut? A Nyloc nut is a hex nut with a nylon insert (a coloured polymer ring) moulded into the top. As the nut is wound onto a bolt, the bolt's threads cut into the nylon, creating friction that resists vibration loosening. Once fitted, the nylon grips the thread and stops the nut backing off under normal vibration and shock loads. They're widely used in machinery, vehicles, marine applications and any assembly subject to vibration. Can a Nyloc nut be reused? Manufacturers recommend single-use. Each time the nut is wound on, the nylon insert deforms, and its locking force drops after the first removal. For safety-critical or vibration-prone joints, fit a new Nyloc nut every time you disassemble the joint. Nyloc Nut Sizes — Metric M3 to M30 Reference — Quick Reference The DIN 985 dimensional reference for the full standard metric range. All sizes use across-flats (AF) measurement equal to a standard hex nut of the same thread, so a 13 mm spanner fits an M8 Nyloc the same as an M8 hex nut. Thread size Across flats (mm) Approx height (mm) Stock at AIMS M3 5.5 4.0 Standard — Bremick zinc, stainless M4 7.0 5.0 Standard M5 8.0 6.0 Standard M6 10.0 7.5 Standard — extremely common M8 13.0 9.5 Standard — extremely common M10 17.0 11.5 Standard M12 19.0 14.0 Standard M14 22.0 16.0 Less common — to order M16 24.0 17.5 Standard M20 30.0 20.5 Heavy-duty — Bremick / Hobson M24 36.0 23.5 To order M30 46.0 28.0 Heavy-duty — Hobson What Is a Nyloc Nut? A Nyloc nut is a hex nut with a nylon (polyamide) ring fitted into the top of the body, designed to grip the threads of a bolt or threaded rod and prevent the joint from loosening under vibration. The nylon insert sits proud of the threaded portion of the nut — when the nut is wound onto a bolt, the bolt thread cuts into the nylon, creating friction that resists rotation in either direction. "Nyloc" is the original brand name (registered to Nyloc Corporation) but is now used generically across the Australian and global fastener industry to describe any hex nut with a nylon insert. You will see the same fastener under several names — all referring to the same product: Nyloc nut — dominant Australian trade term Nylock nut — common spelling variant; sometimes treated as a separate brand but functionally identical Nylon insert lock nut — engineering / technical term used on drawings and specs Stop nut or Elastic stop nut (ESL nut) — older trade language, mostly American origin, occasionally encountered on imported equipment Self-locking nut — generic engineering term that includes Nyloc plus all-metal lock-nut variants This guide covers DIN 985 (the low-profile metric standard, the most common AU stock) and DIN 982 (standard-height variant), the temperature ceiling above which Nyloc nuts stop locking, the reuse question, the materials and grades available at AIMS, the alternatives for applications where a Nyloc is the wrong choice, and the practical decision rules for choosing between them. The full AIMS Nyloc range — Bremick and Hobson stock in metric M4 to M30 plus imperial UNC and UNF, zinc-plated and 304/316 stainless — is available here. How a Nyloc Nut Works — The Prevailing Torque Mechanism A standard hex nut relies entirely on the friction between the bolt threads and the nut threads (plus the clamping load against the joint) to stay tight. Under vibration, that friction can cycle — the nut backs off slightly with each vibration pulse and over time loosens completely. This is the failure mode every wing nut, every standard nut on a vibrating motor, every bolt on a drum kit eventually finds. A Nyloc nut adds a second locking mechanism that does not depend on clamping load. The nylon insert sits in the unthreaded top section of the nut. When the bolt is wound through, the bolt thread engages the nut threads as normal — and then the bolt thread enters the nylon insert. The nylon is slightly under-sized relative to the bolt thread, so it deforms elastically as the thread passes through. The deformation grips the bolt thread, creating prevailing torque — friction that resists rotation independent of the clamping force. "Prevailing torque" simply means the torque required to turn the nut on the bolt before any clamping load develops. A standard hex nut has effectively zero prevailing torque — you can spin it freely down the thread. A Nyloc has prevailing torque from the moment the bolt thread engages the nylon. This is the engineered locking effect, and it is why Nyloc nuts stay tight even when the joint clamping force is reduced or temporarily lost. One practical consequence: installing a Nyloc requires more torque than a standard nut to wind it down. This is correct and intended — it is the prevailing torque doing its job. It is not a sign of cross-threading or a damaged nut. DIN 985 vs DIN 982 — Thin vs Standard Height This is the variant distinction most AU buyers do not realise exists. Two metric standards govern Nyloc nuts, with different overall heights but otherwise identical mechanics. Standard Profile Approx height (M8 example) Stock availability in AU DIN 985 / ISO 10511 Low-profile / thin ~8 mm Standard — dominant AU stock DIN 982 / ISO 7040 Standard / regular height ~10 mm Less common — special-order at most AU suppliers DIN 985 is what AU industrial buyers receive when ordering "M-something Nyloc" without specifying the standard. The thin profile saves height in tight-clearance assemblies and uses less material. DIN 982 has a taller body, slightly higher clamping capacity, and is preferred in heavy-duty or high-vibration applications where the longer thread engagement matters. For most general industrial work the two are functionally interchangeable; for engineered assemblies, follow the drawing specification. Imperial Nyloc nuts to ASME B18.16.6 (UNC and UNF threads) are also stocked at AIMS in 1/4" through 5/8" — common on imported American equipment, marine fittings, and agricultural hardware. Dimensional ratios are similar to DIN 985 — thin-profile is the AU default. Nyloc Nut Sizes — Metric M3 to M30 Reference The DIN 985 dimensional reference for the full standard metric range. All sizes use across-flats (AF) measurement equal to a standard hex nut of the same thread, so a 13 mm spanner fits an M8 Nyloc the same as an M8 hex nut. Thread size Across flats (mm) Approx height (mm) Stock at AIMS M3 5.5 4.0 Standard — Bremick zinc, stainless M4 7.0 5.0 Standard M5 8.0 6.0 Standard M6 10.0 7.5 Standard — extremely common M8 13.0 9.5 Standard — extremely common M10 17.0 11.5 Standard M12 19.0 14.0 Standard M14 22.0 16.0 Less common — to order M16 24.0 17.5 Standard M20 30.0 20.5 Heavy-duty — Bremick / Hobson M24 36.0 23.5 To order M30 46.0 28.0 Heavy-duty — Hobson The most commonly stocked sizes for AU general industrial work are M6, M8, M10, M12 and M16 — covering 80% of the assembly fastening Australian workshops encounter. Larger sizes (M20 through M30) appear in structural, agricultural, and heavy machinery applications. Smaller sizes (M3 through M5) in electronics, light fittings, and precision assembly. For matching bolt grades and the full thread reference, see our Bolt Grade Chart and Fastener Reference Chart. The 120°C Temperature Ceiling — Engineering Warning The single most overlooked specification on a Nyloc nut is the temperature limit of the nylon insert. This is a soft failure mode — the nut does not fall off catastrophically, it just stops working as a lock. Most users do not realise the lock effect has been lost until the joint loosens. Standard nylon (polyamide 6 or polyamide 6/6) used in Nyloc inserts retains its elastic properties between approximately −40°C and +120°C in service. Above 120°C the nylon softens, the prevailing torque grip on the bolt thread reduces, and at sustained service temperatures above 130–140°C the insert deforms permanently. The Nyloc becomes, mechanically, a regular hex nut with a now-useless plastic ring. Engineering warning — do not use a Nyloc near heat sources: Exhaust manifolds, flue connections, kiln components, oven internals, furnace flanges, near combustion chambers, near hot machinery casings, anywhere the joint regularly sees above 100°C in service. Apparent temperature is not the same as service temperature — a flange bolt next to an exhaust pipe can sit well above ambient. When in doubt, measure or err toward all-metal lock nuts (DIN 980, covered later in this guide). The temperature limit also caps Nyloc use in: Engine bay applications above the manifold — block-mounted brackets, turbo support brackets, heat-shield fixings Industrial process equipment — drying ovens, baking lines, polymer extruders Steam systems — flange connections on saturated steam piping above 100°C Foundry equipment — anywhere the working environment is hot ambient Welding fixtures — where the fastener can heat-soak through repeated welding cycles For these applications, switch to an all-metal lock nut (DIN 980 V Stover) — covered in the alternatives section below. Can You Reuse a Nyloc Nut? This is a question with two correct answers — depending on whether you are reading the manufacturer's data sheet or asking the tradesperson on the floor. The manufacturer position — single use Bremick, Hobson, Inox World and the major fastener brands universally publish "single-use" guidance for Nyloc nuts. The first time the bolt threads pass through the nylon insert, they cut a thread profile into the polymer. On removal, the nylon retains that profile but with reduced thickness and reduced elasticity. Each subsequent install/remove cycle reduces locking effectiveness further. By the third or fourth cycle, the insert provides minimal prevailing torque. The field position — depends on application criticality In real-world AU industrial practice, Nyloc reuse is common in non-critical applications. Workshop fixtures, hobby projects, light assembly that gets repeatedly pulled apart and reassembled — Nyloc nuts get reused. The locking effect degrades each cycle, but for low-vibration applications the residual friction is enough. Decision rule The deciding question is: what does failure cost? Application criticality Reuse policy Aviation, structural, lifting equipment, vehicle suspension, brakes Never reuse — replace every time Heavy machinery, vibrating equipment, vehicle drivetrain Replace whenever practical — reuse only in emergency Industrial assembly, machine guards, light vibration Reuse acceptable for one or two cycles; replace if locking feels reduced Workshop fixtures, hobby work, non-critical assembly Reuse common — replace when nylon visibly damaged A practical inspection check before reusing: wind the nut down the bolt by hand. If the threads engage and turn freely until the nylon hits the bolt, and the nylon then provides resistance with a clear "grip" feel, the locking effect is still functional. If the nut spins freely all the way down without resistance, the nylon is no longer effective — replace it. The other practical issue: nylon inserts are destroyed by abrasive grit, paint, rust, or thread debris before installation. A Nyloc that has been left in a dirty workshop drawer or installed on rusty threads will lock once, then fail. Clean threads are critical. Materials and Grades — Class 8, Class 10, 304 and 316 Stainless The Nyloc range at AIMS is matched to the bolt grades it pairs with. The grade rating refers to the strength of the nut body, not the locking effectiveness — the nylon insert is the same across all metal grades. Class 8 zinc-plated (DIN 985) The general-purpose AU industrial default. Class 8 carbon steel body matched to Grade 8.8 bolts, with zinc electroplate finish for moderate corrosion resistance. Suitable for indoor industrial assembly, light outdoor exposure under shelter, and most general fastening. Bremick and Hobson dominate AU stock at AIMS in this category. Class 10 zinc-plated (DIN 985) Higher-strength carbon steel matched to Grade 10.9 bolts. Used where the joint design specifies a Grade 10.9 bolt and the matching higher-strength nut is required. The nylon insert and locking mechanism are identical to the Class 8 version — the upgrade is in the metal body strength, not the locking effect. 304 (A2-70) stainless steel The general-purpose stainless option. Property Class A2-70 — approximately 700 MPa tensile. Suitable for outdoor work away from salt, food processing without chlorides, light marine (sheltered), pharmaceutical, and most outdoor applications where corrosion resistance matters more than maximum strength. 316 (A4-70) stainless steel The marine-grade option. Adds molybdenum for chloride resistance. Specify 316 for marine fittings, coastal industrial sites, swimming pool fittings, food processing brines, and chemical environments. Approximately 30% more expensive than 304. Stainless and Nyloc — galling note: Stainless threads can gall (cold-weld) when wound dry into matching stainless threads. This applies to the metal portion of the Nyloc but not the nylon insert. To prevent galling, apply a thread lubricant or anti-seize to the bolt threads before installation. The nylon portion does not need lubrication — the prevailing torque mechanism still works as designed. For full thread-locking guidance and lubrication options, see our Thread Locking & Sealing Guide. Nyloc Alternatives — When a Different Lock Nut Is the Right Choice Nyloc is not the answer for every vibration-prone joint. Three main alternatives exist in AU supply, each with a defined sweet spot. All-metal lock nuts — DIN 980 V Stover The DIN 980 V (Stover-pattern) all-metal lock nut achieves vibration resistance through metal-on-metal interference rather than a polymer insert. The top section of the nut is slightly distorted from circular — the threads are pressed into a tri-lobular or out-of-round shape. As the bolt winds in, the metal threads of the nut deform elastically against the bolt thread, creating prevailing torque without any nylon involvement. All-metal Stover nuts work at temperatures far above the nylon limit — typically rated to 200°C continuous service, with spike capability to 300°C. They are the correct fastener for: Exhaust system flanges and turbo bracket fastenings Industrial process equipment (kilns, ovens, drying lines, polymer machinery) Steam piping above 100°C service Engine-near applications and drivetrain components Welding fixtures and foundry equipment The trade-offs: higher installation torque (more force required to wind down), higher cost than equivalent Nyloc, and slightly less consistent locking force across multiple installations. They are also tolerant of more reuses than Nyloc — typically rated for 5–10 cycles before locking degrades meaningfully. Serrated flange nuts — DIN 6923 (whiz nuts) A serrated flange nut combines a hex nut, a flat washer-equivalent flange, and a series of radial serrations on the underside of the flange. The serrations bite into the bearing surface as the nut tightens, creating a locking effect from the joint surface rather than from the nut threads. Standard pairing: a high-speed assembly fastener where parts count and assembly time matter more than reusability. Whiz nuts are most commonly seen in automotive bracket assembly, sheet metal fastening, and high-volume production where the integrated washer + locking effect saves an assembly step. They mark the bearing surface (the serrations dig into the workpiece), so they are not appropriate for finished or coated surfaces. Threadlocker — Loctite 243 / 263 / 277 A chemical alternative — apply Loctite (or equivalent threadlocker) to the bolt thread before installation. The threadlocker cures in the absence of air and active metal contact, bonding the thread surfaces and resisting vibration loosening. Loctite is reusable in the sense that you can break the bond, clean the thread, and reapply — but each application is single-use. Threadlocker is the right answer when: The fastener cannot accept a Nyloc geometry (set screws, blind threads, threaded holes) Maximum strength is required and an all-metal lock nut is not feasible The joint needs to seal against fluid as well as resist vibration For the full threadlocker reference covering Loctite grades, application, and removal, see our Thread Locking & Sealing Guide. Vibration resistance hierarchy For comparing the options against application demand: Vibration severity Recommended solution Low — light machinery, light vehicles Nyloc (DIN 985) Moderate — equipment with running motors, drum kits, light engine accessories Nyloc + spring washer, or Nyloc + flat washer + threadlocker High — heavy machinery, vibration-critical assemblies, engine drivetrain All-metal Stover (DIN 980 V) or Nord-Lock washers Critical — aviation, lifting equipment, life-safety All-metal Stover plus threadlocker; engineered solution per spec Above 120°C service temperature All-metal Stover (DIN 980 V) — Nyloc not viable When to Use a Nyloc Nut The right applications for a Nyloc nut share a common pattern: vibration is a real concern, but the joint stays below 100°C in service, the assembly will not need to be disassembled and reassembled many times, and a moderate locking effect (not maximum) is sufficient. Vibration-prone assembly under 100°C — light machinery covers, equipment guards on running motors, panel fastening on vibrating equipment Outdoor and marine fittings (within material rating) — gates, fences, pool fittings, light marine fittings using stainless 304 or 316 Vehicle bodywork and interior — non-engine-bay fastenings where vibration matters Trailer hardware — light fittings, bracket attachments, toolbox mounting Furniture and equipment fitting where the design needs vibration resistance and cost is a factor General industrial assembly — anywhere the joint design assumed prevailing torque locking When NOT to Use a Nyloc Nut Equally important — the situations where a Nyloc will fail or perform below expectation. Above 120°C service temperature. Nylon softens; locking lost. Switch to all-metal Stover. Exhaust systems, manifolds, near hot machinery. Nyloc temperature ceiling makes this category off-limits. Critical aviation and lifting applications. Use engineered all-metal lock nuts to spec; never substitute Nyloc. After multiple reuses on the same nut. The nylon insert degrades each cycle; locking effect approaches zero by install three or four. Replace. Threads contaminated with grit, rust, paint, or debris. Nylon insert is destroyed before the lock effect even develops. Where the bolt does not fully pass through the nylon insert. If the bolt is too short to reach beyond the metal threads of the nut, the nylon never engages — no locking effect. Where the design specifies an all-metal or engineered lock nut. Substitution downgrades the joint. Where the assembly will see chemical attack on nylon. Strong acids, some solvents, and high-concentration ammonia degrade polyamide. Specify stainless body with verified chemical compatibility, or switch to all-metal. AIMS Industrial Nyloc Range and AU Stock The AIMS Nyloc range covers metric and imperial sizes, indoor through marine environments. Browse the full collection at the AIMS Nyloc nut collection or the broader hex lock nuts collection for all-metal alternatives alongside Nyloc options. Metric range — Bremick, Hobson Class 8 zinc-plated DIN 985 — M3 through M30 Class 10 zinc-plated DIN 985 — heavy-duty matched to Grade 10.9 bolts 304 (A2-70) stainless DIN 985 — M3 through M20 316 (A4-70) stainless DIN 985 — M4 through M16, marine and food-processing Imperial range UNC zinc-plated — 1/4" through 5/8" common stock; 9/16" available UNF zinc-plated — 1/4" through 5/8" common stock; 7/16" and 9/16" available UNF zinc-plated thin Nyloc to ASME B18.16 — for legacy and imported equipment All-metal alternatives stocked alongside DIN 980 V Stover-pattern all-metal lock nuts — for high-temperature applications above the Nyloc 120°C limit DIN 6923 / 6927 serrated flange lock nuts — for high-volume sheet-metal and bracket assembly Companion product groups Types of Nuts Guide (Art 65) — full nut family reference covering hex, Nyloc, flange, dome, castle, square, wing Wing Nut Guide (Art 132) — companion deep-dive (the hand-tightened alternative; not vibration-resistant) Socket Head Cap Screw Guide (Art 125) — pairing high-strength bolts with Nyloc Button Head Socket Screw Guide (Art 174) — pairing context Types of Washers Guide (Art 74) — flat and spring washer pairing Thread Locking & Sealing Guide (Art 44) — Loctite alternative to Nyloc Bolt Grade Chart (Art 11) — matching nut grade to bolt grade Frequently Asked Questions What is a Nyloc nut? A Nyloc nut is a hex nut with a nylon (polyamide) ring fitted into the top of the body, designed to grip the threads of a bolt or threaded rod and prevent the joint from loosening under vibration. The nylon insert deforms elastically as the bolt thread passes through, creating prevailing torque (friction independent of clamping load). "Nyloc" is the original brand name (Nyloc Corporation) and is now used generically across the Australian fastener industry. Also called Nylock nut, nylon insert lock nut, stop nut, or elastic stop nut. What is a Nyloc nut used for? Nyloc nuts are used wherever a threaded joint needs to resist vibration loosening at temperatures below 120°C. Common applications include light machinery covers, equipment guards on running motors, vehicle bodywork (non-engine-bay), trailer hardware, marine fittings (using stainless 316), pool fittings, gate hardware, furniture, light industrial assembly, and any joint where the design specifies prevailing torque locking. They are not appropriate for high-temperature applications (exhaust, manifolds, kilns) or critical aviation and lifting equipment, where all-metal lock nuts (DIN 980) are required. What's the difference between a Nyloc nut and a regular hex nut? A regular hex nut relies entirely on thread friction and joint clamping load to stay tight. Under vibration, that friction can cycle and the nut backs off slightly with each pulse, eventually loosening completely. A Nyloc nut adds a nylon insert at the top of the body that grips the bolt thread independently of clamping load — creating prevailing torque (friction that resists rotation regardless of joint load). The Nyloc stays tight under vibration where a regular hex nut will loosen. What's the difference between DIN 985 and DIN 982 Nyloc nuts? Both are metric Nyloc nut standards with identical locking mechanisms — the difference is the overall height. DIN 985 (also called ISO 10511) is the low-profile / thin variant — the AU industrial default. DIN 982 (ISO 7040) is the standard / regular-height variant with a taller body and slightly more thread engagement. DIN 985 is what AU buyers receive when ordering "M-something Nyloc" without specifying. DIN 982 is preferred in heavy-duty or high-vibration applications where longer thread engagement matters; it is less commonly stocked in AU general supply. What temperature can a Nyloc nut withstand? Standard nylon (polyamide 6 or 6/6) used in Nyloc inserts retains elasticity between approximately −40°C and +120°C in service. Above 120°C the nylon softens, the prevailing torque grip on the bolt thread reduces, and at sustained service above 130–140°C the insert deforms permanently. Above this point, the Nyloc becomes mechanically a regular hex nut with a useless plastic ring — the locking effect is lost. For applications above 100°C in service, switch to an all-metal lock nut (DIN 980 V Stover-pattern), which is rated to roughly 200°C continuous service. Can Nyloc nuts be reused? Manufacturer guidance is single-use — Bremick, Hobson and the major fastener brands universally recommend replacing Nyloc nuts after one install/remove cycle. The first time the bolt thread cuts through the nylon, it creates a thread profile in the polymer; each subsequent cycle reduces locking effectiveness further. Field practice varies by application criticality — workshop and hobby assembly often reuses Nyloc nuts without issue, but vehicle suspension, lifting equipment, structural and aviation applications should always replace. Practical inspection: if the nut spins freely down the bolt without nylon resistance, the lock effect is gone — replace. How does a Nyloc nut work? The nylon insert at the top of the nut sits in an unthreaded section of the body. When a bolt is wound through the nut, the bolt thread engages the metal threads first as normal, and then enters the nylon insert. The nylon is slightly under-sized relative to the bolt thread, so it deforms elastically as the thread passes through. The deformed nylon grips the bolt thread, creating prevailing torque (friction that resists rotation independently of clamping load). This is why Nyloc nuts stay tight under vibration even when the joint clamping force is reduced or temporarily lost. What's the Australian standard for Nyloc nuts? There is no AS/NZS-specific Nyloc nut standard. Australian industrial supply universally references the international standards: DIN 985 / ISO 10511 for the low-profile (thin) metric variant, and DIN 982 / ISO 7040 for the standard-height metric variant. ASME B18.16 covers the imperial UNC/UNF Nyloc nuts seen on imported American equipment. Property class designation follows the same numbering as standard hex nuts (Class 8, Class 10) for carbon steel and A2-70 / A4-70 for stainless. What's the difference between a Nyloc nut and an all-metal lock nut? A Nyloc nut achieves vibration resistance through a nylon insert that grips the bolt thread by elastic deformation. An all-metal lock nut (typically DIN 980 V Stover-pattern) achieves the same effect through metal-on-metal interference — the top section of the nut is slightly distorted from circular, so the metal threads themselves deform elastically against the bolt thread. Key differences: all-metal nuts work at much higher temperatures (rated to 200°C continuous service vs Nyloc's 120°C limit), tolerate more reuses (5–10 cycles vs single-use), require higher installation torque, and cost more. Choose all-metal for high-temperature, heavy-vibration, or critical applications; choose Nyloc for general industrial work below 120°C where cost matters. What size Nyloc nut do I need for an M8 bolt? An M8 bolt takes an M8 Nyloc nut. The metric thread sizing is identical between bolt and nut. An M8 Nyloc to DIN 985 has a 13 mm across-flats (AF) hex measurement — the same as a standard M8 hex nut, so a 13 mm spanner fits both. Approximate body height is 9.5 mm. Match the property class to the bolt grade — Class 8 nut for Grade 8.8 bolt, Class 10 nut for Grade 10.9 bolt. Are Nyloc nuts available in stainless steel? Yes — both 304 (A2-70) and 316 (A4-70) stainless are widely stocked. Choose 304 for general indoor and most outdoor applications away from salt water; choose 316 for marine, coastal industrial sites within roughly 1 km of the surf, swimming pool fittings, food processing brines, and chemical environments. AIMS holds metric M3 through M16 in 316 stainless and a wider range in 304. Apply anti-seize to the bolt thread before installation to prevent stainless thread galling — the nylon portion of the Nyloc does not need lubrication. Can a Nyloc nut be used outdoors? Yes — provided the material is matched to the environment. Zinc-plated carbon steel Nyloc is suitable for sheltered outdoor and most light outdoor use; for full weather exposure choose 304 stainless; for marine, coastal industrial within 1 km of surf, swimming pool fittings or chemical environments, choose 316 stainless. The nylon insert itself is unaffected by normal outdoor exposure — UV degradation of the insert is minor over typical service life. Ensure the threads are clean before installation; outdoor applications often expose threads to grit and rust that destroys the nylon insert before locking can develop. What are the other names for a Nyloc nut? Several names refer to the same fastener: Nyloc nut (dominant Australian trade term, after Nyloc Corporation), Nylock nut (common spelling variant), nylon insert lock nut (engineering term), nylon insert nut, stop nut and elastic stop nut (older trade language, mostly American), ESL nut (engineering abbreviation), and self-locking nut (generic engineering term that also covers all-metal alternatives). On AU industrial drawings and parts lists, "Nyloc" or "DIN 985" are the most common designations. How tight should a Nyloc nut be tightened? Tighten a Nyloc nut to the same torque as a standard hex nut of the same size and grade — the nylon insert does not change the recommended tightening torque. The locking effect is independent of clamping load. Note that installing a Nyloc requires more torque than a standard nut to wind it down (because the nylon grip resists rotation from the moment the bolt thread engages the insert) — this is correct and intended, the prevailing torque mechanism doing its job. The final clamping torque is what matches the standard nut spec; the additional run-down torque is the locking effect engaging. When should I NOT use a Nyloc nut? Avoid Nyloc nuts in applications above 120°C service temperature (exhaust systems, manifolds, kilns, ovens, near hot machinery), in critical aviation and lifting equipment where engineered all-metal lock nuts are required by spec, where the bolt is too short to fully pass through the nylon insert (the lock effect needs the bolt thread to enter the insert), where threads are contaminated with grit / rust / paint / debris (the nylon insert is destroyed before locking develops), where the assembly will see chemical attack on nylon (strong acids, some solvents, high-concentration ammonia), and after multiple reuses where the nylon has degraded. For above-120°C service, switch to all-metal Stover (DIN 980 V); for chemical exposure, switch to stainless body with verified compatibility or all-metal lock nut. Need the right spanner for that bolt? Our Spanner Size Chart lists every common metric and imperial size. Pair this with our Metric Bolt Size Guide for the thread pitch, AF dimension and grade options at every common size. People Also Ask — Nyloc Nuts Q: What is a nyloc nut used for? A nyloc nut (nylon insert lock nut) is used wherever vibration or movement could cause a standard nut to loosen over time. The nylon insert grips the bolt thread, resisting self-loosening without thread adhesive. Common applications include automotive, machinery, conveyor systems, and any assembly subject to cyclic loading or vibration. Q: How many times can a nyloc nut be reused? Nyloc nuts are designed for single use. Each removal cycle deforms the nylon insert slightly, reducing its locking grip. For safety-critical or high-vibration assemblies, always fit a new nyloc nut. In low-load, non-critical applications careful reuse is sometimes accepted, but replacing with a new nut is the recommended practice. Q: What is the difference between a nyloc nut and a standard hex nut? A standard hex nut relies on friction between thread surfaces alone and can loosen under vibration. A nyloc nut adds a nylon insert at the top that deforms around the bolt thread, providing positive locking resistance. Nyloc nuts require greater installation torque and maintain their clamping force much better under dynamic or vibrating loads. Q: Can nyloc nuts be used at high temperatures? No — the nylon insert softens above approximately 80–90°C, significantly reducing its locking effectiveness. For elevated-temperature applications such as engine bays, exhaust components, or industrial ovens, use all-metal prevailing-torque lock nuts (serrated flange or distorted thread types) instead of nyloc nuts. Q: What grades and materials are nyloc nuts available in? Nyloc nuts are available in Class 5 through Class 10 property classes in carbon steel, and in stainless steel grades 304 and 316 for corrosion-resistant applications. Marine, food processing, and outdoor environments typically use stainless 316. Match the nut grade to the bolt grade — never mix grades in a structural joint. For bin and hopper flow-aid hardware, browse the AIMS industrial pneumatic vibrator range (ball, piston, and turbine). For die nuts, see our die nuts range stocked across Australia.
Read moreButton Head Socket Screw Guide: ISO 7380-1 vs 7380-2, Sizes, Torque Limits & When to Use
For more engineering reference charts and selection tables, see our Engineering Reference Charts hub — covering fasteners, bearings, lubrication, measuring, welding and Australian standards. What Is a Button Head Socket Screw? A button head socket screw is a low-profile threaded fastener with a rounded dome head and an internal hex (Allen) socket drive. It is sometimes called a button head cap screw in spec sheets and engineering drawings, or abbreviated to BHCS on parts lists. Australian product catalogues — including the AIMS Industrial range — generally refer to these as button head socket screws or button head socket cap screws. The geometry is the defining feature. A standard socket head cap screw to DIN 912 / ISO 4762 has a tall cylindrical head whose height equals the thread diameter — an M8 cap head is 8 mm tall. A button head to ISO 7380-1 has a low rounded dome whose height is approximately half the thread diameter — an M8 button head is around 4 mm tall. The hex socket sits inside this shorter head, which means the socket itself is shallower than a cap head's. The head profile is the engineering trade-off: lower profile, less snag risk, more cosmetic appeal — at the cost of clamping force, drive engagement and torque ceiling. This guide covers the ISO 7380-1 (Style A — flat under-head) and ISO 7380-2 (Style B — flanged collar) variants, the dimensional reference, the engineering reasons button heads should not be substituted for socket head cap screws in clamp-critical joints, the materials and grades available at AIMS, and the AU applications where button head socket screws are exactly the right choice. The AIMS button head range — Inox World 316 stainless, Bremick Class 10.9 zinc-plated, Champion assortment kits, plain steel and 304 stainless — is available here. Button Head vs Socket Head Cap Screw — The Engineering Trade-Off The button head and the socket head cap screw share the same drive (hex socket / Allen key) and the same metric thread sizes. They are not, however, mechanically equivalent. The difference lies in the head — and the head is where button heads fail first. Specification Socket head cap screw (DIN 912) Button head socket screw (ISO 7380-1) Head profile Tall cylindrical Low rounded dome Head height (M-thread × multiplier) ~1.0 × thread diameter ~0.5 × thread diameter M8 example — head height 8.0 mm ~4.4 mm M8 example — head diameter 13.0 mm 14.0 mm Hex socket size (across flats) 6 mm (deeper socket) 5 mm (shallower socket) Hex key engagement depth Full — high cam-out resistance Reduced — earlier cam-out under torque Approximate torque ceiling vs cap head 100% (reference) ~60–70% Standard property class supplied Class 12.9 black oxide Class 10.9 zinc-plated; some 12.9 black oxide Best for Engineered joints, dies, gearbox covers, structural fastening Light fastening, covers, panels, T-slot, cosmetic finish The torque ceiling reduction is geometric, not metallurgical. A Class 12.9 button head and a Class 12.9 cap head have the same metallurgy — same tensile strength, same yield, same hardness. They fail at different torques because the button head's reduced head height means a shallower hex socket, less Allen key contact area, and a thinner head cross-section above the threaded shank. The bit cams out earlier; the head shears at lower torque. If a drawing specifies "M8 SHCS Class 12.9", the joint design assumes the higher torque ceiling and clamping force of a cap head. Substituting a button head into that joint reduces clamping capacity by 30–40% — enough to cause vibration loosening, fatigue, or outright failure depending on the application. Never substitute. If the drawing is unclear, get clarification before ordering. ISO 7380-1 vs ISO 7380-2 — Style A Flat vs Style B Flanged This is the variant that most AU supplier copy glosses over. Two distinct ISO 7380 styles exist, and they perform meaningfully differently. ISO 7380-1 — Style A (flat under-head) The standard button head. Flat under-head bearing surface meeting the threaded shank at a sharp transition. Sized M3 through M16. The under-head bearing area is essentially the head diameter minus the thread diameter — a relatively small annular ring. For most general fastening this is fine; for soft surfaces, painted finishes, or thin sheet, the load concentrates and can mark or dimple the workpiece without a flat washer. ISO 7380-2 — Style B (flanged with integrated collar) The flanged variant — a wider integrated collar around the under-head, effectively a built-in flat washer. The collar increases the under-head bearing area substantially, distributing clamping load over a larger contact patch. This eliminates the need for a separate flat washer in many applications and improves load distribution on softer or thinner materials. Feature ISO 7380-1 (Style A) ISO 7380-2 (Style B flanged) Under-head profile Flat — small annular bearing Flanged collar — integrated washer Bearing surface area Standard ~30–50% larger Need for separate flat washer Recommended on soft surfaces Often eliminated Best for Hard surfaces, machined joints Soft surfaces, painted finishes, thin panels, T-slot Stock availability Standard — full M3 to M16 Common — typically M3 to M12 Choose ISO 7380-1 for hard-on-hard fastening where bearing area is not a concern. Choose ISO 7380-2 when the workpiece is soft (aluminium extrusion, painted steel, plastic) or where the integrated collar replaces a separate washer in production assembly. For T-slot aluminium extrusion (covered later), the flanged ISO 7380-2 is often the better fit. Button Head Dimensions — M3 to M16 Reference The dimensional reference for ISO 7380-1 button head socket screws across the standard metric range. Hex socket size is the size of the Allen key required — see our Allen Key & Hex Key Guide for full driver guidance. Thread size Head height (mm) Head diameter (mm) Hex socket size (Allen key) Common stock length range M3 1.65 5.7 2 mm 4 – 30 mm M4 2.20 7.6 2.5 mm 5 – 40 mm M5 2.75 9.5 3 mm 6 – 50 mm M6 3.30 10.5 4 mm 8 – 70 mm M8 4.40 14.0 5 mm 10 – 100 mm M10 5.50 17.5 6 mm 12 – 100 mm M12 6.60 21.0 8 mm 16 – 100 mm M14 7.70 24.0 10 mm 20 – 80 mm (limited stock) M16 8.80 27.5 10 mm 25 – 80 mm (limited stock) Three observations from this table that matter in practice: The 0.5d head height rule — head height is approximately half the thread diameter on every size. This is the simple physical reason the torque ceiling is lower than a cap head (head height = full thread diameter on DIN 912). The hex key is one size smaller than the equivalent cap head — an M8 button head takes a 5 mm Allen key; an M8 cap head takes a 6 mm Allen key. Buyers reaching for the "M8 size" Allen key out of habit will often find it does not seat in the button head socket. Match the bit to the recess, not to the thread. Stock availability tapers above M12 — M14 and M16 button heads are special-order at most AU industrial suppliers. If your design needs a larger button head, factor in lead time. AIMS holds the M3 to M12 range as standard with M14 / M16 to order. Why Button Heads Fail — The Engineering Warning Most generic supplier articles describe button heads as "lower torque" without explaining where the failure actually happens. The engineering forums (Practical Machinist, Eng-Tips, AskEngineers) are blunter: "Screws such as button socket heads will often fail in the head before the thread. Typical hex head capscrews must NOT fail in the head." — Practical Machinist forum, engineering tradition A properly designed cap head fastener fails in the threaded shank under tensile overload — the shank stretches, yields, then breaks, and the head remains intact. The engineer can see the failure, the head pulls cleanly out, and the joint signals what happened. A button head, by contrast, often fails at the head — the dome shears off around the socket recess, leaving the threaded shank stuck in the workpiece and a piece of debris where the bit was. The failure is harder to see, harder to diagnose, and harder to remove. Three geometric reasons drive this failure mode: Reduced cross-section above the thread. The button head's low profile means there is less material between the top of the threaded shank and the bottom of the hex socket. Under tensile load this thinner cross-section becomes the weak link. Stress concentration at the socket walls. The shallow socket has thin walls — a stress riser around the recess where the shear plane forms when the head fails. Smaller hex socket leverages less torque. The Allen key contacts a smaller area against shallower walls. Cam-out happens earlier; the bit slips before reaching cap-head torques. Engineering warning: Do not specify a button head socket screw for any joint where the original design specified a socket head cap screw, structural bolt, or hex bolt. The button head's torque ceiling is approximately 60–70% of the equivalent cap head, and the failure mode (head shears around socket) is unpredictable and hard to inspect. If clamping force, vibration resistance, or structural integrity matters — use a cap head. Use button head only where the joint design accommodates the lower performance. Class 10.9 Button Heads — The Recess-Wear Story (Not Strength) Here is a counterintuitive engineering point that buyers regularly miss. Class 10.9 button head socket screws exist in the AU supply chain — Bremick stocks them, Champion supplies them, AIMS holds them — but the reason they exist is not what most buyers assume. The grade upgrade from Class 8.8 to Class 10.9 in a button head is primarily about wear resistance of the hex socket recess, not about joint strength. The harder steel in a 10.9 button head resists rounding of the socket walls under high power-driver torque — useful in production assembly where the same fastener might be installed thousands of times across a manufacturing line. The head still fails at lower torque than a Class 10.9 cap head; the metallurgy is identical but the geometry is not. If the joint genuinely needs Class 10.9 strength, you need a Class 10.9 cap head — not a Class 10.9 button head. The grade label looks the same; the mechanical performance is not. This is the kind of detail that is easy to miss and expensive to learn after a joint fails. For full grade reference covering 8.8, 10.9 and 12.9 across all socket-driven fasteners, see our Bolt Grade Chart. Materials — Plain Steel, Zinc-Plated, 304 and 316 Stainless The AIMS button head socket screw range covers four core materials — chosen to match real AU industrial use cases rather than offering exotic specifications that rarely move stock. Plain (uncoated) carbon steel Used where the assembly will be painted, powder-coated or otherwise finished after fastening, or where the corrosion environment is benign and short-lived. Plain steel button heads will rust in any moisture exposure — they are not suitable for outdoor or unprotected use. Zinc-plated carbon steel (Class 10.9) The general-purpose default. Class 10.9 carbon steel with a zinc electroplate finish, typically clear or yellow passivated. Suitable for indoor industrial assembly, light outdoor use under shelter, and equipment exposed to incidental moisture. The zinc coating gives moderate corrosion resistance for indoor and protected applications. Bremick is the dominant AU brand in this category at AIMS. 304 (A2-70) stainless steel The general-purpose stainless option. Property Class A2-70 — approximately 700 MPa tensile, 450 MPa yield. Suitable for outdoor work away from salt, food processing without chlorides, light marine (sheltered), pharmaceutical, and most wet indoor applications. Roughly equivalent to a Class 8.8 carbon steel screw in mechanical strength but with significantly better corrosion resistance. 316 (A4-70) stainless steel The marine-grade option. Adds molybdenum to the 304 chemistry for resistance to chloride attack. Specify 316 for marine fittings, coastal industrial sites within roughly 1 km of the surf, swimming pool fittings, food processing brines, and chemical environments. Approximately 30% more expensive than 304 and worth every cent in the right environment. Inox World is the dominant AU brand in this category at AIMS. Stainless and galling: Stainless threads — particularly 316 in 316 — are prone to galling (cold-welding the threads together as friction heats them during installation). This is the single most common failure mode of stainless button head socket screws in service. The fix is simple: apply a thread lubricant or anti-seize compound to stainless threads before installation. Never install stainless dry into a stainless thread. For applications where threadlocker is required, see our Thread Locking & Sealing Guide. What Button Heads Are Actually For — Design Intent Reading this article so far you might be wondering why anyone uses a button head at all, given the strength compromise. The answer is that button heads are not designed to compete with cap heads on strength — they are designed to do something cap heads cannot: Eliminate snag points. The smooth dome profile gives no edges to catch on clothing, gloves, hoses, harnesses, or moving parts. Critical on equipment guards, machine covers, and any operator-touch surface. Reduce sharp-edge hazards. The rounded head has no machined corners that can cut hands during cleaning, maintenance, or operation. Touch-safety on access panels and removable covers. Provide a finished cosmetic profile. The dome is visually softer than a cylindrical cap head — preferred on visible fastening in furniture, retail fittings, exposed panels. Save head height. Where a cap head would protrude too far, the lower-profile button head fits without counterboring. Useful in tight clearances and aesthetic finishing. Pair with T-slot extrusion. The button head + T-nut combination is the engineered solution for fastening to aluminium extrusion frames. A correctly chosen button head solves problems a cap head cannot. The trade-off is that you must accept the lower torque ceiling — and design the joint around it. Common Australian Applications T-slot aluminium extrusion (Bosch Rexroth, Misumi, generic 20/30/40-series profiles) This is the application where button head socket screws genuinely shine. T-slot aluminium extrusion frames — used in industrial automation builds, lab benches, machine guards, robotics frames, custom CNC machinery, and modular workshop fixtures — are designed around the button head + T-nut connection. The T-nut slides into the extrusion's T-slot from the end (or drops in via a special profile), the bracket or panel sits over the slot, and the button head socket screw threads into the T-nut from above, clamping the bracket against the extrusion face. The button head's low profile sits flush with or slightly proud of the bracket surface, eliminating snag risk on the equipment frame. The flanged ISO 7380-2 variant is often preferred here — the integrated collar protects the soft aluminium surface from being marked. Standard sizes for AU T-slot work: 20-series profiles — M5 button head 30-series profiles — M6 or M8 button head 40-series profiles — M8 button head Imperial 80/20 series (American spec) — 1/4"-20 button head (where used in AU on imported machinery) Electronics and rack-mount equipment Server hardware, 19-inch rack equipment, professional audio gear, networking switches, and computer enclosures use button head socket screws extensively. The low profile clears adjacent components and panel slots; the cosmetic dome looks finished on visible installation. M3 and M4 dominate; M5 and M6 for heavier rack hardware. Machine guards and access panels Removable covers, hinged guards, vented panels — anywhere an operator regularly touches the equipment surface. The button head's snag-free profile reduces hand-injury risk during cleaning and maintenance. Class 10.9 zinc-plated dominates; stainless on food-processing or chemically exposed equipment. 3D printing, makerspace and custom fabrication The maker community defaults to button head socket screws for 3D printer hardware, custom fabrication, hobby robotics, and DIY fixturing. The aesthetic dome, the wide range of stainless options (304 / 316), and the T-slot extrusion compatibility make button heads the standard fastener for printer kits like Voron, Prusa, RepRap, and Bambu builds. M3 and M5 in 304 stainless dominate. Robotics and industrial automation Pneumatic frames, robot end-effectors, vision-system mounts, sensor brackets — anywhere automation hardware bolts to T-slot or sheet-metal subframes. Button head + T-nut is the standard automation connection. M5 and M6 dominate. Furniture, retail fittings and decorative hardware The dome profile is more visually finished than a cylindrical cap head — preferred on visible fastening in cabinets, display fixtures, commercial fitouts, and architectural metalwork. Stainless 304 for indoor; 316 where moisture or chemicals are present. Drive Options — Hex Socket vs Torx Button Head Standard button head socket screws use a hex socket (Allen key) drive — the recess is a hexagonal hole in the centre of the dome. This is the default and what AIMS stocks across the full range. Torx-driven button head variants exist — the recess is a six-lobe star instead of a hex hole. Torx button heads provide better cam-out resistance under high-torque power-driver assembly, useful in production lines where the bit cycle count matters. They are less commonly stocked in AU general supply but available to order. For full driver and bit reference: Hex (Allen) drive: See our Allen Key & Hex Key Guide for sizing, ball-end vs flat tip, T-handle vs L-handle, and torque ratings. Torx drive: See our Torx Bit Sizes Guide for the full T-series sizing, security Torx, and Torx Plus variants. AIMS Industrial Button Head Range — Brands and Stock The AIMS button head socket screw range covers indoor general-purpose work through marine and food-processing applications. Browse the full button head socket screw collection here. Bremick Australian-owned fastener supplier — broad metric DIN 7380 / ISO 7380-1 button head range in Class 10.9 zinc-plated and Class 12.9 black oxide. M3 through M12 standard; larger sizes to order. The general-purpose default for AU industrial assembly. Inox World Stainless-only specialist — full A2 (304) and A4 (316) button head socket screw range in metric M3 through M12. Used wherever corrosion resistance is the primary requirement: marine, food processing, pharmaceutical, outdoor coastal, swimming pools, chemical environments. Property class A2-70 / A4-70 marked on every part. Champion Specialty assortment kits and individual sizes. The Champion CA1420 124-piece button head socket cap screw assortment kit covers M4 through M8 in common lengths, useful for workshop top-up stock or maintenance kits where multiple sizes are required. Single-size SKUs and assortments Beyond the brand ranges, AIMS holds single-size box quantities (typically 25 or 100 per box) across plain, zinc-plated, 304 and 316 finishes. For high-volume production work or non-standard sizes (M14, M16, longer lengths), special-order through the AIMS Industrial team. Companion product groups Socket Head Cap Screw Guide (Art 125) — DIN 912 sister article covering the high-torque standard cap head Countersunk Screw Guide (Art 97) — ISO 10642 flush-fit socket-driven family member Screw Head Types Guide (Art 126) — full head-shape reference covering all variants Types of Nuts Guide (Art 65) — including T-nut variants for extrusion connections Types of Washers Guide (Art 74) — pairing flat and spring washers with button head fastening Frequently Asked Questions What is a button head socket screw? A button head socket screw is a low-profile threaded fastener with a rounded dome head and an internal hex (Allen) socket drive. It is sometimes called a button head cap screw or abbreviated to BHCS. The head is approximately half the height of a standard socket head cap screw of the same thread size, giving a smoother, less obtrusive finish — at the cost of a lower torque ceiling and smaller hex socket. Standardised under ISO 7380-1 (Style A flat) and ISO 7380-2 (Style B flanged with collar). What is the difference between a button head and a socket head cap screw? Both share the same hex (Allen) drive and the same metric thread sizes. The difference is the head. A socket head cap screw (DIN 912) has a tall cylindrical head whose height equals the thread diameter and a deep hex socket. A button head socket screw (ISO 7380-1) has a low rounded dome whose height is approximately half the thread diameter and a shallower hex socket. The button head's torque ceiling is roughly 60–70% of the equivalent cap head, and the head can shear around the socket under overload. Cap head for engineered joints; button head for light fastening, cosmetic finish, T-slot extrusion and snag-free covers. What is the difference between ISO 7380-1 and ISO 7380-2? ISO 7380-1 (Style A) is the standard flat-under-head button head with a small annular bearing surface meeting the threaded shank. ISO 7380-2 (Style B) adds a flanged collar around the under-head — effectively an integrated flat washer that increases the bearing area by 30 to 50 percent. The flanged variant distributes clamping load over a wider contact patch, eliminating the need for a separate washer in many applications and protecting soft surfaces (aluminium extrusion, painted steel, plastic). Both share identical thread sizes and head height; the difference is the under-head bearing geometry. What is the difference between a pan head and a button head screw? A pan head has a flat top with slightly rounded edges and is generally driven with a Phillips, Pozi, Torx or slotted recess. A button head has a fully rounded dome top and is generally driven with a hex socket (Allen key). The drive is the more practical difference — button head means socket-driven; pan head means cross- or slotted-driven. Both have lower head profiles than a socket head cap screw, but the button head's deeper hex socket gives better torque transfer than a Phillips pan head. For full head shape comparison, see our Screw Head Types Guide. What size hex key does an M8 button head socket screw take? An M8 button head socket screw to ISO 7380-1 takes a 5 mm Allen key (hex key). Note this is one size smaller than the equivalent M8 socket head cap screw, which takes a 6 mm Allen key. Other common sizes: M3 = 2 mm, M4 = 2.5 mm, M5 = 3 mm, M6 = 4 mm, M8 = 5 mm, M10 = 6 mm, M12 = 8 mm. The smaller socket is a direct result of the lower head height — there is less material to machine the recess into. Are button head socket screws as strong as socket head cap screws? No — even when both are the same property class. The metallurgy is identical (a Class 12.9 button head and a Class 12.9 cap head have the same tensile strength, yield, and hardness), but the head geometry is not. The button head's reduced head height creates a thinner cross-section above the threaded shank and a shallower hex socket, both of which lower the torque ceiling. In practice, a button head fails at approximately 60–70% of the torque a cap head will accept, and the failure mode (head shearing around the socket recess) is harder to predict and inspect than a cap head's clean shank failure. Why does Class 10.9 button head exist if the head is the weak point? Because the grade upgrade in a button head primarily improves the wear resistance of the hex socket recess — not the joint strength. The harder steel in a Class 10.9 button head resists rounding of the socket walls under high power-driver torque, useful in production assembly where the same fastener might be installed thousands of times. The head still fails at lower torque than a Class 10.9 cap head; the metallurgy is the same, the geometry is not. If a joint genuinely needs Class 10.9 strength, specify a Class 10.9 cap head, not a button head. What is BHCS? BHCS stands for Button Head Cap Screw — the engineering abbreviation used on parts lists, drawings, and specification documents. In Australian product catalogues you will more often see "button head socket screw" or "button head socket cap screw" in full. All terms refer to the same fastener: a low-profile, dome-headed, hex-socket-driven screw to ISO 7380-1 or ISO 7380-2. Can I use a button head where the drawing specifies a socket head cap screw? No. The drawing specification reflects the joint design — including the assumed clamping force, torque, and failure mode. Substituting a button head reduces clamping capacity by approximately 30–40 percent and changes the failure mode (head shearing rather than shank yielding). For any structural, vibration-prone, or clamp-critical joint, this substitution is unsafe. If the drawing specifies SHCS or DIN 912, supply DIN 912. If the drawing is unclear, request clarification before ordering. Substitution is only acceptable when the application is genuinely light-duty (covers, panels, cosmetic fastening) and the specification is informal. What torque can I apply to a button head socket screw? Approximately 60–70 percent of the torque rating for an equivalent socket head cap screw of the same property class and thread size. As an indicative reference for Class 10.9 button heads: M5 around 6 Nm, M6 around 10 Nm, M8 around 25 Nm, M10 around 50 Nm, M12 around 85 Nm (dry threads, no anti-seize). Reduce by 15–20 percent for lubricated threads. These are guidelines only — always defer to the equipment manufacturer's specified torque if one is given, and never push button heads to cap-head torques. What are button head socket screws used for? Button head socket screws are used wherever a low-profile, snag-free, cosmetically finished hex-socket-driven fastener is needed. Standard applications include T-slot aluminium extrusion frames (Bosch Rexroth, Misumi, 80/20 and similar), electronics and rack-mount equipment, machine guards and removable access panels, 3D printing and makerspace hardware, robotics and industrial automation, furniture and retail fittings, and any place where the rounded dome reduces hand-injury or snag risk. They are not appropriate for clamp-critical engineered joints — those need a socket head cap screw. What size button head socket screws fit 80/20 T-slot aluminium extrusion? It depends on the profile series. For 20-series metric T-slot profiles (20mm × 20mm and similar), M5 button heads are standard. For 30-series profiles, M6 or M8. For 40-series profiles (heavier industrial frames), M8 button heads. American 80/20 imperial profiles use 1/4"-20 button head + T-nut combinations. The flanged ISO 7380-2 variant is often preferred for T-slot applications because the integrated collar protects the soft aluminium surface from being marked under clamping load. Are button head socket screws available in stainless steel? Yes — both A2 (304) and A4 (316) stainless are widely stocked. Choose 304 for general indoor and most outdoor applications away from salt water; choose 316 for marine, coastal industrial sites within roughly 1 km of the surf, swimming pool fittings, food processing brines, and chemical environments. AIMS holds the Inox World 316 stainless range across M3 through M12 in standard lengths, plus 304 stainless in plain finish. Always lubricate stainless threads before installation to prevent galling. Can a button head socket screw be flush-mounted in a counterbore? Generally no — that is what countersunk socket screws (ISO 10642 / DIN 7991 — see our Countersunk Screw Guide) are designed for. A button head's domed top will not sit flush in a flat-bottomed counterbore — it will leave the dome proud of the surface. If you need a flush finish, specify a countersunk socket screw. If you need the button head dome but want the head recessed below the surface, you can counterbore deeper than the head height — but this is unusual and generally indicates the wrong fastener has been chosen. What's the difference between a flat (countersunk) and button head socket screw? Both are socket-driven (hex / Allen key). The flat or countersunk socket screw (ISO 10642 / DIN 7991) has a conical underside and a flat top — designed to sit fully flush with the work surface in a matching countersunk hole. The button head socket screw (ISO 7380-1) has a flat under-head and a rounded dome top — designed to sit proud of the surface with a low, snag-free profile. Flat for flush mounting; button head for low-profile but visible mounting. Both have lower torque ceilings than a standard socket head cap screw — the cap head remains the strongest of the three. The matching socket and drive size live in our Socket Size Chart — every common fastener head covered. People Also Ask — Button Head Socket Screws Q: What is a button head socket screw and how does it differ from a socket head cap screw? A button head socket screw (BHCS) has a low dome-shaped head — approximately half the height of a socket head cap screw of the same thread size — providing a lower profile and a smooth, rounded appearance. It is used where head height is a constraint or aesthetics matter. Q: What is the difference between ISO 7380-1 and ISO 7380-2 button head screws? ISO 7380-1 is the standard flat-base button head. ISO 7380-2 adds an integral flange under the head, providing a larger bearing area, better load distribution, and reduced risk of pull-through in softer parent materials such as aluminium or plastics. Q: Why are button head socket screws not suitable for high-torque structural joints? The hex socket in a button head is shallower than in a cap screw of the same thread — this limits the torque that can be applied before the socket reams out. Button heads are engineered for lower-load, aesthetic, and panel-fastening applications, not structural joints. Q: What materials are button head socket screws available in? Button heads are typically available in plain (black oxide) steel, zinc-plated steel, 304 stainless, and 316 stainless. Material selection is driven by the corrosion environment and the strength required; 316 stainless is preferred for marine and chemical exposure. Q: When is a Torx drive button head preferred over a hex socket button head? Torx drive provides a larger tool-engagement surface than hex, reducing cam-out risk during power-tool assembly. It is preferred on production lines or wherever high assembly speed and consistent torque are needed without risking socket damage.
Read moreTorx Bit Sizes Guide
Yes — "Torx" and "star bit" refer to the same six-pointed star drive geometry. "Torx" is the trademarked brand name developed by Camcar Textron in 1967; "star bit" or "star drive" is the common Australian and UK casual term for the same six-lobe drive (covered by ISO 10664). On engineering drawings the abbreviation TX is used. Be careful not to confuse Torx with Pentalobe (five-point, used by Apple) or Hex Plus (Wera's enhanced hex drive) — both can look star-shaped but are NOT Torx-compatible. The simplest visual check is to count the points: six = Torx, five = Pentalobe. For more engineering reference charts and selection tables, see our Engineering Reference Charts hub — covering fasteners, bearings, lubrication, measuring, welding and Australian standards. Torx vs Star vs Other Star-Shaped Drives — Quick Reference Drive Points Same as Torx? Torx (TX) 6 Yes — this IS Torx Star bit / star drive 6 Yes — common AU casual name for Torx Torx Plus (IP) 6 (squared lobes) Refined Torx — bits cross-compatible with reduced contact Security Torx (TR) 6 + centre pin Standard Torx with tamper-resistant pin — needs hollow bit Pentalobe (P) 5 NO — Apple proprietary, not interchangeable Hex Plus (Wera) 6 flats (not points) NO — enhanced hex/Allen, different geometry Tri-wing 3 NO — security drive, not related to Torx What Is a Torx Bit? A Torx bit is a screwdriver bit with a six-pointed star-shaped tip, designed to engage a matching six-lobe recess in a fastener head. The Torx system was developed in 1967 by Camcar Textron (now Acument Intellectual Properties) as a high-torque alternative to Phillips and slotted drives. It is patented and trademarked — "Torx" is the brand name; the underlying geometry is technically a "six-lobe drive" and is covered by ISO 10664. In Australian workshops, Torx is most commonly called Torx by tradespeople familiar with the brand, and star bit or star drive in casual conversation — particularly on building sites where the bit category matters more than the brand. On engineering drawings the abbreviation is TX followed by the size number, e.g. "TX25". All three terms refer to the same six-lobe drive geometry. Torx sizing uses a T-number for internal drives (T10, T15, T20, T25, T30, T40 etc.) where the bit fits into a recess in the screw head, and an E-number for external drives (E6, E8, E10 etc.) where the screw or bolt has a six-lobe external profile and the bit is a socket that fits over the head. The numbering systems are independent — an E8 external Torx is roughly equivalent to a T40 internal Torx, not a T8 — which is one of the most common buying errors in the category. This guide covers internal Torx (T-series), external Torx (E-series), Torx Plus, security Torx, and the proprietary lookalikes (Pentalobe, Hex Plus) that get confused with standard Torx. AIMS holds the full Sutton, Ko-Ken, Wera and Wiha Torx range — see torx screwdrivers and screwdriver bits. Why Torx? Drive Comparison vs Phillips, Pozi and Hex Torx exists because the older drive systems have a fundamental geometric weakness: their drive surfaces are angled in a way that converts torque into cam-out — the bit lifts out of the recess under load, stripping the head. Phillips drives were originally designed with intentional cam-out (to limit overtightening on early production lines), but on a high-torque modern power driver, that "feature" becomes a defect. Torx is engineered for the opposite outcome. The six lobes contact the bit at six points, the contact surfaces are nearly perpendicular to the rotation direction, and there is almost no axial force component. The bit stays seated under load — torque transfers cleanly into the screw rather than lifting the bit out of the head. Drive style Cam-out resistance Strip resistance Best for Phillips (PH) Low — designed to cam out Low Light electrical, electronics, where torque limit matters Pozidriv (PZ) Medium Medium European joinery, cabinet hardware Robertson (square) High High Timber screws (AU/NZ/Canada) Hex socket (Allen) Very high High (the recess can round) High-torque machine fastening, cap screws Torx (TX) Very high Very high General modern fastening — best overall drive External hex N/A (external) Highest Structural, heavy machinery The Reddit consensus across r/Tools, r/DIY and r/Construction is consistent: for stripping resistance and torque transfer with internal drives, Torx is the best general-purpose choice. The only drives that beat it on raw strip resistance are external (visible spanner-driven heads), and the only situations where Phillips genuinely wins are intentional torque-limited assembly. For a complete drive comparison covering every major recess type and how to identify them on existing fasteners, see our Screwdriver Types Guide. Torx Size Chart — T1 to T100 Torx sizing runs from T1 (smaller than a pencil tip, used in micro-electronics) through T100 (used in heavy industrial machinery and earthmoving equipment). The point-to-point diameter — the dimension across opposite lobes — increases with the T-number. Torx size Approx point-to-point (mm) Common application T1 – T6 0.81 – 1.75 mm Mobile phones, watches, micro-electronics T7 2.0 mm Laptops, small electronics T8 2.31 mm Hard drives, electronics enclosures T9 2.5 mm Light electrical fittings T10 2.74 mm Computer cases, light automotive trim T15 3.27 mm Automotive interior trim, light fixtures T20 3.86 mm Decking screws, light timber, automotive T25 4.43 mm Decking screws, structural timber, brake calipers T27 4.99 mm Automotive disc rotors, suspension components T30 5.52 mm Heavy decking, structural timber, automotive bolts T35 6.65 mm Specialty automotive, motorcycle hardware T40 6.65 mm Automotive engine, gearbox, structural metal T45 7.82 mm Heavy automotive, light industrial T50 8.83 mm Heavy machinery, structural connections T55 11.22 mm Heavy industrial fastening T60 13.25 mm Heavy machinery, earthmoving equipment T70 15.51 mm Specialised heavy industrial T80 17.54 mm Mining, heavy plant T100 22.13 mm Largest standard Torx — heavy plant, marine The most commonly stocked sizes in Australian general supply are T10, T15, T20, T25, T27, T30, T40 and T45. A standard 8-piece or 10-piece Torx bit set will cover this range and handle 90% of fastening jobs an AU tradesperson encounters. If a screw drive looks like Torx but a T-number bit will not fit cleanly, check whether you are looking at an external Torx (E-series), a Torx Plus, a security Torx with a centre pin, or a non-Torx lookalike (Pentalobe, Hex Plus, tri-wing). Each has its own bit type — covered in the sections below. Internal Torx (T) vs External Torx (E) Internal and external Torx are completely different products that share the same lobe geometry but operate in opposite directions. Internal Torx (T-series) The bit is a small star-shaped tip that fits into a recess in the screw head. The fastener head has a six-lobe hole; the bit fills it. Standard sizing: T1, T2, T3 ... T100. This is the more common form and the type most people mean when they say "Torx". External Torx (E-series) The bit is a socket with a six-lobe internal profile that fits over a six-lobe boss on the bolt or screw head. The fastener has a star-shaped head; the bit is a socket that envelops it. External Torx sizing uses an E-prefix: E5, E6, E7, E8, E10, E12, E14, E16, E18, E20, E24. Critical buying trap: External Torx (E) sizes do not correspond to internal Torx (T) sizes of the same number. An E8 external Torx is roughly equivalent to a T40 internal Torx — not a T8. The two numbering systems are independent. Buying E-series tooling assuming the numbers match T-series will give you the wrong size every time. Always confirm whether a fastener requires internal or external Torx, then specify by the correct prefix. External Torx Approximate equivalent internal Torx Common application E5 ~T25 Light automotive components E6 ~T30 Automotive trim, brake hardware E8 ~T40 Engine bolts, automotive structural E10 ~T50 Heavy automotive, suspension E12 ~T55 Engine bay structural E14 ~T60 Heavy machinery E18 ~T70 Heavy industrial E24 ~T100 Heaviest standard external Torx External Torx is most commonly seen in European automotive engineering — engine block bolts, transmission casings, brake caliper mountings — where the high-torque transfer of an external profile combines with the strip resistance of the Torx geometry. Mercedes, BMW, Audi, and Volvo specify external Torx widely. Torx Plus — The Engineered Upgrade (IP / EP) Torx Plus is a refinement of the standard Torx geometry, introduced when the original Torx patent expired in the early 1990s. The lobes are squared off and the drive angle is reduced from 15° (standard Torx) to 0° (Torx Plus). The result is a bit profile with greater contact area, lower stress concentration, and noticeably higher torque transfer before deformation. Specification Standard Torx Torx Plus Drive angle 15° 0° Lobe shape Rounded Squared Contact area Standard Up to 25% greater Cam-out under high torque Possible at extreme torque Almost nil Internal sizing prefix T (e.g. T25) IP (e.g. IP25) External sizing prefix E (e.g. E8) EP (e.g. EP8) Best for General fastening High-precision CNC, production assembly, aerospace Compatibility: A standard Torx bit will fit into a Torx Plus screw recess — but with reduced contact area and somewhat compromised torque transfer. It works but you will not get the full benefit. A Torx Plus bit will not fit a standard Torx screw recess properly — the squared lobes do not match the rounded profile. If a fastener is specified as Torx Plus (IP25, IP30, EP8 etc.), source the matching Torx Plus bit. If specified as standard Torx, either type will work. Torx Plus is most commonly encountered in high-end automotive (premium European brands), aerospace, medical devices, and CNC production environments where the marginal performance gain matters. Security Torx — Tamper-Resistant with Centre Pin (TR) Security Torx — also called Tamper-Resistant Torx or Torx TR — is a standard Torx recess with a small post in the centre of the star. The centre pin prevents a standard solid Torx bit from being inserted, requiring a security Torx bit with a corresponding hole drilled through the centre to clear the pin. Sizing follows the same T-number convention as standard Torx, with an "S" suffix or "TR" prefix to indicate the security version: T15S, T20S, T25S, T30S etc. (sometimes written TR15, TR20). Where security Torx is used Public infrastructure — bus seating, signage, public toilets, transit fittings Retail security — anti-theft brackets, display fixtures, point-of-sale hardware Electronics enclosures — gaming consoles, set-top boxes, equipment that should not be opened by users School and laboratory equipment — preventing unauthorised disassembly Vehicle anti-theft — number plate fixings, badge mountings, security panels Strength trade-off: Security Torx bits are hollowed in the centre to clear the pin. This makes the bit shaft mechanically weaker than a solid (non-security) Torx bit of the same size. For high-torque applications where security is not required, use a non-security Torx bit — they are stronger, less prone to twisting under load, and longer-lasting. Reserve security bits for the situations that actually require them. Compatibility — important A security Torx bit (with the centre hole) will fit a standard non-security Torx screw — it just has a hollow centre that does not engage anything. So a security Torx bit set covers both security and standard Torx fasteners, at the cost of slightly weaker bit shafts. A standard Torx bit will not fit a security Torx screw — the solid centre of the bit clashes with the screw's centre pin. If you do not know in advance which type you will encounter (e.g. servicing public infrastructure, school equipment, or retail fixtures), specify a security Torx bit set — it covers both. AIMS holds Sutton S113 Tamper Resistant Torx inserts and Ko-Ken security Torx bits — search the screwdriver bits collection. Torx Is Not the Same as Pentalobe or Hex Plus Several proprietary drive systems look superficially similar to Torx but are not compatible. Confusion is common — at quick glance they all look like a six-pointed star — and using the wrong bit will round out the recess. Pentalobe (5-point) Apple's proprietary drive used on iPhones, MacBooks, and other Apple devices. It has five lobes instead of six. A Torx bit will not fit a Pentalobe recess and a Pentalobe driver will not fit a Torx recess. The visual cue: count the points. Five = Pentalobe; six = Torx. Pentalobe drivers are sold as P2, P5, P6 etc. — not interchangeable with anything else. Hex Plus (Wera) Wera's enhanced hex driver geometry. It is not Torx — it is an upgraded six-flat (hex / Allen) drive with rounded contact corners. Hex Plus bits are stamped "Hex Plus" or "HEX-PLUS" by Wera and have a slightly different cross-section to standard hex. A standard hex bit will fit a Hex Plus recess; a Hex Plus bit will fit a standard hex socket. Confusion arises because both Hex Plus and Torx are marketed as "anti-cam-out" — they solve the same problem with different geometries. Tri-wing, Tri-groove, Spanner head Other security / specialty drives that look star-like but use different geometries. Tri-wing has three asymmetric points; tri-groove has three grooves (used in firearms, gaming hardware); spanner head has two pin holes (used in security applications). All require their own dedicated bits — none are Torx-compatible. For the security-head overview, see our Screw Head Types Guide, which covers the security drive family alongside the head shapes. Choosing the Right Torx Bit — Insert, Impact and Hand Driver "Torx bit" is a category that includes several physical formats. The right choice depends on the tool you are driving with and the torque you intend to apply. 1/4-inch hex shank insert bits The standard format — a short bit with a 1/4" hex shank that fits into screwdriver bit holders, magnetic adapters, and the chuck of a power drill or impact driver. Most Torx bits sold in Australia are this format. The Sutton S111 series (CRV inserts) is a typical example — 25 mm long, hardened chrome-vanadium steel, 1/4" hex shank. Available individually and in sets covering T10 through T40. Impact-rated bits (for impact drivers) Standard insert bits will fracture or twist under the cycling torque of an impact driver. Impact-rated Torx bits use harder steel alloys and a torsion zone — a section of the bit shaft engineered to flex slightly under impact loading, dissipating shock that would otherwise crack the tip. Sutton S169 (Ultrabit) and S212 / S214 (Supatorq) are the AU industrial impact options. Ko-Ken impact Torx bits are also stocked. Use impact-rated bits exclusively in impact drivers; standard bits will not survive. Long-reach bits and power bits For applications where the screw is recessed below the surface — counterbored holes, deck screws driven through joists, automotive engine bay fasteners — extended-length Torx bits are required. Common lengths: 50 mm, 75 mm, 100 mm, 150 mm. Sutton holds the AU range; Wera and Wiha offer longer specialty lengths. Hand drivers — T-handle and screwdriver-style For repeated assembly or in confined spaces, dedicated Torx hand drivers are often more efficient than a bit + holder. A T-handle Torx driver gives high torque from a balanced grip; a standard screwdriver-style handle is lighter and faster for lower-torque work. AIMS holds the Sutton range and the Ko-Ken impact-style screwdriver bits — see the torx screwdrivers collection. Sockets and ratchet drives (for E-series) External Torx is driven by a socket on a 1/4", 3/8", or 1/2" ratchet — same as a standard hex socket but with a six-lobe internal profile instead of six flats. AIMS stocks Ko-Ken external Torx sockets in the common automotive sizes (E8 through E20). Common Torx Applications in Australian Work Decking and structural timber screws The most significant shift in AU construction over the last decade has been the move from Pozidriv to Torx on decking and structural timber screws. Premium brands — Macsim, Spax, Klein, and most Class 3 and Class 4 timber screws — are now supplied with T20, T25, or T30 Torx drive. The reason is power-driver compatibility: a Pozi bit cams out of the head under the high cycling torque of a modern impact driver; a Torx bit holds. T25 is the most common decking screw size in AU domestic construction; T30 for heavier structural work. Automotive — interior and powertrain European automotive (BMW, Audi, Mercedes, Volvo, VW) uses Torx widely throughout interior trim, dash panels, brake hardware, and powertrain components. T15 to T30 dominates interior work; T40 to T55 typical for engine and gearbox structural; external Torx (E10 to E20) for engine block and transmission bolts. Japanese and Korean vehicles increasingly adopting Torx — Nissan, Toyota, Hyundai, Kia all use T15 / T20 / T25 in modern interior trim. Electronics and IT hardware T6 through T10 dominate laptops, monitors, gaming consoles, and small electronics. Server hardware uses T15 widely. Specialty pin-in (security) Torx is common on customer-facing equipment to deter unauthorised opening. Public infrastructure and retail Security Torx (T15S to T30S) used widely on bus seating, train fittings, retail display fixtures, public toilets, signage, vehicle plates, and any fixture that needs to resist tampering by passing public. Bicycle, motorcycle and outdoor gear High-end bicycle components (Shimano, SRAM) use T25 / T30 widely on disc brake mounts and chainring bolts. Motorcycle bodywork increasingly Torx-driven. Outdoor gear (camping equipment, bike racks, rooftop tents) often Torx for vibration resistance. AIMS Industrial Torx Range — Brands and Stock The AIMS Torx range covers individual bits, sets, hand drivers, impact-rated tooling, and specialty long-reach bits. Key brands stocked: Sutton Australian-owned tooling specialist with a deep AIMS-stocked range: Sutton S111 — standard Torx insert bits, CRV (chrome-vanadium) construction, 25 mm length, 1/4" hex shank. Sizes T10 through T40. The general-purpose AU workshop bit. Sutton S113 — tamper-resistant (security) Torx insert bits, CRV. The same dimensions as S111 but with the centre hole for security Torx fasteners. Sutton S169 Ultrabit — impact-rated Torx insert bits with torsion zone. Up to 12× the life of a standard bit in impact-driver work. Sutton S212 Supatorq — Custom S8 steel power bit, 1/4" hex shank, impact-rated for high-torque applications. Sutton S214 Supatorq — same Custom S8 steel platform with security Torx-S geometry, 150 mm long-reach option for deep-recessed fastenings. Ko-Ken Japanese precision tooling specialist, particularly strong in impact-rated and socket products: 1/4" drive Torx screwdriver bits — full T-series and TR (security) range Impact-rated Torx bits — sizes including T45 long-reach for automotive applications External Torx sockets — E8 through E20 in 1/4" and 3/8" drive for engine and gearbox work Champion Specialty fastener tooling — tamper-resistant Torx and security driver kits. The Champion family includes the OWS-RT One-Way Screw Removal Tool used widely by locksmiths and security technicians. Wera and Wiha German precision tooling — premium specialty Torx bits for production, aerospace, and CNC environments. Available to order. Browse the full range: Torx screwdrivers | Screwdriver bits. For the broader drive-recess context covering all bit types, see our Screwdriver Types Guide. For the head-shape companion, see our Screw Head Types Guide. Frequently Asked Questions What is a Torx bit? A Torx bit is a screwdriver bit with a six-pointed star-shaped tip designed to engage a matching six-lobe recess in a fastener head. The system was developed by Camcar Textron in 1967 as a high-torque alternative to Phillips and slotted drives. "Torx" is the brand name; the underlying geometry is a six-lobe drive covered by ISO 10664. In Australian shop language it is also called a "star bit" or "star drive" — all three terms refer to the same thing. What sizes do Torx bits come in? Internal Torx bits are sized from T1 (smaller than a pencil tip, used in micro-electronics) through T100 (heavy industrial machinery). The most commonly stocked sizes in Australian general supply are T10, T15, T20, T25, T27, T30, T40 and T45 — these handle 90% of the fastening jobs an AU tradesperson encounters. External Torx (E-series) uses an independent numbering system from E5 through E24 — these do not correspond to T-series numbers. Is a star bit the same as a Torx bit? Yes — "star bit" or "star drive" is the common Australian and UK casual term for a Torx bit. "Torx" is the trademarked brand name; the underlying six-lobe geometry is the same regardless of which term you use. On engineering drawings the abbreviation TX (e.g. TX25) is also used. Be careful not to confuse Torx with Pentalobe (5-point, used by Apple) or Hex Plus (Wera's enhanced hex drive) — both can look similar at a glance but are not Torx-compatible. How do I know what Torx size I need? The fastener manufacturer or equipment manual is the best source. If you do not have that, the practical method is to try bits from a Torx set in order, starting one size smaller than your visual estimate and moving up. The correct Torx size will fully seat in the recess with no rocking and no gap; if the bit feels loose or rocks, go up one size. If it will not enter the recess, go down one size. Common decking screws are T25 or T30; computer hardware T8 or T10; automotive interior trim T15 to T30. What's the difference between Torx and Torx Plus? Torx Plus is a refined version of the original Torx geometry developed when the original patent expired. The drive angle is reduced from 15 degrees to 0 degrees and the lobes are squared off, giving up to 25 percent greater contact area and almost nil cam-out under high torque. Sizing uses an IP prefix for internal Torx Plus (IP25, IP30) and EP for external (EP8). A standard Torx bit will fit a Torx Plus recess with reduced contact, but a Torx Plus bit will not properly fit a standard Torx recess. Torx Plus is most commonly seen in premium automotive, aerospace, and CNC production environments. What's the difference between internal Torx (T) and external Torx (E)? Internal Torx (T-series) is a recess in the screw head — the bit is a small star tip that fits into the head. External Torx (E-series) is a six-lobe profile on the outside of the bolt head — the bit is a socket that fits over the head, like a hex socket. The numbering systems are independent — an E8 external Torx is roughly equivalent to a T40 internal Torx, not a T8. Always confirm whether a fastener requires internal or external Torx, then specify by the correct prefix. Buying assumption errors here are the most common Torx purchasing mistake. What is a security Torx bit? A security Torx bit — also called Tamper-Resistant Torx or Torx TR — is a Torx bit with a hole drilled through the centre to clear a small pin in the centre of a security Torx fastener recess. The pin prevents a standard solid Torx bit from being inserted, deterring unauthorised tampering. Security Torx bits will fit both security and standard Torx fasteners (the centre hole simply has nothing to engage on a standard fastener), but standard Torx bits will not fit a security Torx fastener. Common applications include public infrastructure, retail security, electronics enclosures, school equipment, and vehicle anti-theft fittings. Is Torx Plus the same as security Torx? No — these are commonly confused but completely different products. Torx Plus is a refined geometry with squared lobes and a 0-degree drive angle, designed for higher torque and lower cam-out — sizing uses IP and EP prefixes. Security Torx (TR) is a standard Torx geometry with a centre pin in the fastener and a hollow centre in the bit, designed to prevent unauthorised disassembly — sizing uses an S suffix or TR prefix. Torx Plus has no security feature; security Torx has no enhanced geometry. Different problems, different solutions. Why are Torx screws better than Phillips? Torx geometry distributes drive torque across six points with contact surfaces nearly perpendicular to the rotation direction — there is almost no axial force component lifting the bit out of the recess. Phillips drives have angled contact surfaces that intentionally cam out under high torque (originally a feature for early production line torque limiting; now a defect on modern impact drivers). The result: Torx is dramatically more strip-resistant than Phillips, particularly under power-driver work. The Reddit and tradesperson consensus is consistent: Torx is the best general-purpose internal drive for stripping resistance and torque transfer. Can a regular Torx bit fit a security Torx screw? No. The pin in the centre of a security Torx recess prevents a standard solid Torx bit from seating fully. You need a security Torx bit (with a corresponding hole drilled through the centre to clear the pin) to engage a security Torx screw. The reverse works: a security Torx bit will fit a standard non-security Torx screw, because the centre hole simply has nothing to engage. If you are servicing equipment where you do not know in advance which type you will encounter, specify a security Torx bit set — it covers both, at the cost of slightly weaker bit shafts due to the hollow centre. What's the difference between Torx and Pentalobe? Torx has six lobes; Pentalobe has five. Pentalobe is Apple's proprietary drive used on iPhones, MacBooks, and other Apple devices, sized as P2, P5, P6 etc. The two systems are visually similar at a glance — both are star-shaped — but they are not interchangeable. A Torx bit will not engage a Pentalobe recess and vice versa. The simplest visual check is to count the points: five points means Pentalobe; six points means Torx. Pentalobe drivers are sold separately and are not stocked in standard Torx bit sets. Are Torx bits compatible with impact drivers? Standard Torx insert bits are not — they will fracture or twist under the cycling torque of an impact driver. Impact-rated Torx bits use harder steel alloys and a torsion zone (a section of the bit shaft engineered to flex slightly under impact loading) to dissipate shock that would otherwise crack the tip. Sutton S169 Ultrabit, S212 Supatorq, and Ko-Ken impact Torx bits are the AU industrial standards for impact-driver work. Always use impact-rated bits in impact drivers — using a standard insert bit in an impact driver is a guaranteed bit failure within minutes. Cross-reference our Socket Size Chart when sizing a socket — metric, SAE, drive size and all. People Also Ask — Torx Bits Q: What is the difference between Torx and Torx Plus (IP) screws? Standard Torx screws have a 6-pointed star profile with straight lobe walls. Torx Plus screws (also called IP — Internal Plus) have a similar star shape but with modified lobe geometry that provides more contact area between the bit and fastener, allowing more torque before the bit cams out. Torx Plus bits and Torx Plus fasteners are not fully interchangeable with standard Torx — a standard T25 bit will not properly seat in a T25 IP fastener, and vice versa. Torx Plus is preferred in high-volume production assembly where fasteners are driven repeatedly and reduced bit and fastener wear is important. Q: What is a security Torx bit and how do I know if I need one? A security Torx fastener (tamper-resistant Torx) has a small pin in the centre of the star recess that prevents a standard Torx bit from seating. These are used by manufacturers to discourage disassembly — common applications include consumer electronics, automotive trim, and safety-critical assemblies. To drive a security Torx fastener, you need a security Torx bit with a corresponding hole in its tip to clear the centre pin. Security Torx bits are sold individually and in sets and are marked with the prefix TR (tamper-resistant) alongside the T-number designation. Q: How do I know which Torx size to use? The correct Torx size is the one that fits snugly in the fastener recess with no play. A bit that is slightly too small will fit but will slip and round out the recess under load. If the original size is unknown, start with the smallest bit that seats firmly without rocking. Common sizes by application: T6–T10 for electronics and small appliances; T20, T25, T27, T30 for automotive (door trim, underbody components, brake callipers); T40 and above for larger structural fasteners. In automotive work, a set covering T10 through T60 handles the vast majority of Torx fasteners encountered. Q: Are Torx bits interchangeable between different brands? Yes — Torx is a standardised profile documented in international standards, so a T25 bit from any reputable manufacturer fits a T25 fastener correctly. However, bit quality varies significantly between manufacturers. High-quality industrial-grade bits are made from harder steel with precise heat treatment and maintain their tip geometry through thousands of drive cycles. Lower-quality bits may fit initially but wear rapidly, leading to cam-out and fastener damage. For professional use, investing in quality industrial tool brands pays off in fastener integrity and bit longevity over the working life of the set. Q: Can I use a Torx bit in an impact driver? Standard screwdriver-type Torx bits can be used in an impact driver for light-duty work, but for heavy-duty impact use — automotive assembly, structural fastening, high-torque applications — purpose-made impact-rated Torx bits should be used. Impact-rated bits are made from more flexible steel such as S2 with a torsion zone that absorbs the shock pulses of the impact driver without fracturing. Standard bits can crack or shatter under sustained impact loading, which is a safety hazard. Impact-rated bits are usually identified by their black oxide finish and impact labelling on the packaging, distinguishing them from chrome-finished standard bits. AIMS Industrial stocks hex power bits — see the full range for trade and industrial use. For torx power bits, see our torx power bits range stocked across Australia.
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Read moreScrew Head Types: Pan, Button, Truss & Countersunk
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. Screw Head Shapes — Quick Reference The screw head families you will see most often in AU industrial supply, in rough order of stock volume: For the full metric bolt range — M3 through M24, thread pitches, head dimensions and grade markings — see the AIMS Metric Bolt Size Guide. Head shape Profile Bearing area Sits flush? Typical drive Best for Pan Slightly rounded top, flat underside Medium No — proud Phillips, Pozi, Torx, hex socket General machine screws, electrical, light assembly Button Low-profile rounded dome Medium-wide No — proud, but low Hex socket, Torx Light fastening, decorative, clearance-limited Truss (mushroom) Wide low dome, very flat Wide No — proud, very low Phillips, Pozi, hex socket Sheet metal, soft materials, large bearing area Countersunk (flat / CSK) Conical underside, flat top Tapered into hole Yes — flush Phillips, Pozi, Torx, hex socket, slotted Flush-fit, hinges, structural steel, no-snag surfaces Raised countersunk (oval) Conical underside, domed top Tapered into hole Sub-flush — domed top proud Phillips, Pozi, slotted Decorative flush — joinery, cabinet hardware Dome / round Tall hemispherical dome Narrow No — proud, tall Slotted, Phillips Decorative, traditional, electrical terminals Cheese / fillister Cylindrical, flat top Narrow No — proud, tall and narrow Slotted, Phillips, hex socket Engineering machine screws, instrumentation Hex (external) Six flats, external drive Wide No — proud, requires spanner Spanner / socket Structural, heavy machinery, high-torque Cap head (SHCS) Tall cylindrical, internal hex Narrow but tall No (or recessed in counterbore) Hex socket (Allen) Precision engineering, dies, jigs (Class 12.9 standard) Bugle Curved transition into countersunk Self-countersinks Yes — flush Phillips, Pozi, square (Robertson), Torx Drywall, decking, soft timber Wafer Very flat, slightly domed Wide and low No — but minimal proud Phillips, Pozi, hex socket Metal framing, Tek sheet-to-frame fastening What Head Shape Does — and Why It Matters Walk into any AIMS Industrial counter and ask for "screws", and the first question back is rarely "what diameter?" or "what length?" — it's "what head?". The shape of the head determines more about how a screw performs than almost any other dimension. It controls the bearing area against the workpiece, whether the head sits proud or flush with the surface, what driver tool engages it, how much torque it can take before the drive strips, and whether the joint can be hidden, decorative, sealed, or tamper-resistant. For hand-tightened fasteners where no driver is required — guards, access panels, jig setups and instrument covers — see the dedicated thumb screw types and sizing guide for knurled, wing and T-handle profiles. This guide compares every screw head type you will encounter in Australian industrial and trade work — pan head, button head, truss head, countersunk (flat), raised countersunk, dome, cheese, fillister, bugle, wafer, hex, hex flange, cap head, and the security variants. We cover what each is designed for, where the trade-offs sit, and how to choose the right head for the job. The companion to this article is our Screwdriver Types Guide, which covers the drive recess (Phillips, Pozi, Torx, hex socket, Robertson and so on). Head shape and drive style are independent decisions — for example, a pan head can be ordered with Phillips, Pozi, Torx, slotted, or hex socket drives. Get the head right first, then choose the drive. The Core Screw Head Shapes — Quick Reference The screw head families you will see most often in AU industrial supply, in rough order of stock volume: For the full metric bolt range — M3 through M24, thread pitches, head dimensions and grade markings — see the AIMS Metric Bolt Size Guide. Head shape Profile Bearing area Sits flush? Typical drive Best for Pan Slightly rounded top, flat underside Medium No — proud Phillips, Pozi, Torx, hex socket General machine screws, electrical, light assembly Button Low-profile rounded dome Medium-wide No — proud, but low Hex socket, Torx Light fastening, decorative, clearance-limited Truss (mushroom) Wide low dome, very flat Wide No — proud, very low Phillips, Pozi, hex socket Sheet metal, soft materials, large bearing area Countersunk (flat / CSK) Conical underside, flat top Tapered into hole Yes — flush Phillips, Pozi, Torx, hex socket, slotted Flush-fit, hinges, structural steel, no-snag surfaces Raised countersunk (oval) Conical underside, domed top Tapered into hole Sub-flush — domed top proud Phillips, Pozi, slotted Decorative flush — joinery, cabinet hardware Dome / round Tall hemispherical dome Narrow No — proud, tall Slotted, Phillips Decorative, traditional, electrical terminals Cheese / fillister Cylindrical, flat top Narrow No — proud, tall and narrow Slotted, Phillips, hex socket Engineering machine screws, instrumentation Hex (external) Six flats, external drive Wide No — proud, requires spanner Spanner / socket Structural, heavy machinery, high-torque Cap head (SHCS) Tall cylindrical, internal hex Narrow but tall No (or recessed in counterbore) Hex socket (Allen) Precision engineering, dies, jigs (Class 12.9 standard) Bugle Curved transition into countersunk Self-countersinks Yes — flush Phillips, Pozi, square (Robertson), Torx Drywall, decking, soft timber Wafer Very flat, slightly domed Wide and low No — but minimal proud Phillips, Pozi, hex socket Metal framing, Tek sheet-to-frame fastening Two practical decision rules from this table: If the head needs to sit flush with the surface, you have three options: countersunk (CSK), bugle, or a cap head used in a counterbored hole. Everything else sits proud. If the material is thin sheet, soft, or you are worried about pull-through (the head punching through the work), you want truss, wafer, or bugle — the wide-bearing low-profile heads. Pan and button concentrate load on a smaller area and can dimple thin sheet. Pan Head — The Workshop Default The pan head is named for its resemblance to an upside-down frying pan: a flat circular underside, slightly raised flat top, and softly rounded edges. It is the most common machine screw head you will encounter in general industrial and electrical work. AIMS stocks pan head screws across the full metric range in Phillips, Pozi, Torx and slotted drives, in carbon steel, 304 stainless, and 316 stainless. Where pan heads excel General assembly — control panels, light brackets, enclosures, electrical terminals. Through-bolting straight (non-tapered) holes — the flat underside seats squarely on a flat clearance hole. Do not use a pan head in a tapered countersunk hole; it will not sit flush and the loading will be uneven. High-torque drive applications — the head profile gives the drive bit good engagement against the head walls. Compared with button or truss, the pan head can take more drive torque before the bit cams out or the drive strips. Fastening to soft materials when bearing area is sufficient — for thin sheet, look at truss or wafer instead. Pan heads work fine on wood, plastic, and standard sheet thicknesses. Where pan heads fall short Pan heads sit proud of the surface — they will catch on garments, hands, or moving parts and they are not appropriate where flush mounting matters. They have less bearing area than truss or wafer, so in very thin sheet or soft material they can pull through under load. And they are not particularly decorative; for visible joinery work, a raised countersunk or button head is usually preferred. Stock sizes at AIMS span M2 through M16 in pan head, with M3, M4, M5 and M6 the most commonly stocked. Lengths from 4 mm to 60 mm are standard. For bulk packs and DIN 7985 (Phillips) or ISO 14583 (Torx) compliance specifications, see the pan head screws collection. Button Head — Low-Profile Rounded The button head (technically Button Head Cap Screw, BHCS) is a low-profile rounded dome with a flat underside. It is most commonly produced as a socket-driven machine screw to DIN 7380 / ISO 7380, with a hex socket in the top of the dome. The standard alternative is a Torx-driven button head, increasingly common in production assembly. AIMS stocks button heads in Class 10.9 zinc-plated, Class 12.9 black oxide, and 304 / 316 stainless — see button head socket screws. Where button heads excel Clearance-limited installations — the low dome profile gives roughly half the head height of a cap head (DIN 912), useful where a tall head would interfere with adjacent components. Cosmetic / decorative finishing — the smooth rounded dome is more visually finished than a pan or hex head. Common on furniture, equipment guards, retail fittings. Light to medium fastening — works well in joints where the clamping load is moderate. Important limitation — torque rating Button heads have approximately 30–40% lower torque rating than equivalent cap head (DIN 912) socket head cap screws of the same diameter and grade. The reason is the shallower hex socket — there is less contact area between the Allen key and the head walls. For the same M8 thread size, a button head's hex socket is around half the depth of a cap head's. Apply too much torque and the socket strips or the bit cams out. If you need the strength of an Allen-driven precision fastener, use a cap head — see our Socket Head Cap Screw Guide for the full DIN 912 reference. Use button head only where clearance, appearance, or light loading make it appropriate. Button head vs round head — terminology gotcha In some trade circles, particularly machining and engineering, "round head" specifically means a screwdriver-driven (slotted, Phillips, Pozi) rounded screw — typically an older or decorative fastener — while "button head" specifically means a socket-driven (Allen) version. In supplier catalogues and in this guide, "button head" is reserved for the DIN 7380 / ISO 7380 socket-driven type. If a parts list calls out a "round head", confirm the drive style before ordering. Truss Head — The Wide-Bearing "Mushroom" The truss head — also called mushroom head in some Australian trades and oven head in older US references — is a low, wide dome with a flat underside, considerably broader than a pan head and lower in profile than a button. It is designed for one purpose: maximum bearing area against a surface, with minimum head height proud of that surface. Where truss heads excel Thin sheet metal fastening — the wide flat underside spreads clamping load across a larger area than a pan or button head, dramatically reducing the risk of dimpling, pull-through, or tearing the sheet. Metal framing screws — 20-gauge steel studs and tracks, ducting, light steel construction. The truss head holds the sheet flat against the frame without pulling the metal up around the head. Soft materials (plastic, soft timber, plasterboard backing) — wide bearing distributes clamping force, lowering the chance of crushing or denting the substrate. Cabinet and equipment closure — where a smooth low-profile finish is wanted but full flush-fit is not required. Warning — torque rating: Truss heads have a noticeably thinner head profile than pan or button heads, which means they have a lower torque rating before the drive strips or the head shears off. This is a real failure mode in production assembly — over-torqued truss heads break at the head/shank junction. Use the wide bearing area for clamping; do not use the truss head as a high-torque fastener. If you need the bearing area of a truss head and high torque, you are choosing the wrong fastener — consider a flange-head or a pan head with a separate flat washer. Australian terminology In Australia, "truss head" is the most common term in product catalogues and engineering. "Mushroom head" appears in some trades, particularly fabrication. "Oven head" is rare in AU usage — more common in older US specifications. All three names refer to the same shape. Countersunk (Flat / CSK) Head — Flush-Fit The countersunk head — abbreviated CSK in AU engineering, often called a flat head in trade contexts — has a conical underside that tapers to match a corresponding countersunk hole in the workpiece. When fully driven, the flat top of the head sits flush with (or below) the surface, leaving no protruding fastener. This is the only way to achieve a truly flush-mounted machine screw. The conical underside is the fastener; the matching countersink in the hole is the seat. Together they distribute clamping load radially outward, making CSK fasteners particularly resistant to shear forces — which is why they are standard in hinges, machinery guards, structural steel, handrails, and any application where a protruding head would be a snag hazard or clearance problem. The 90° vs 82° question The included angle of the conical head is the most important specification — and the most common source of fitting errors. In Australia and Europe, the metric ISO/DIN standard is 90° (ISO 10642, DIN 7991, ISO 7046, DIN 965). In North America, the imperial ASME standard is 82° (ASME B18.6.3). Mixing them results in the screw sitting proud of the surface or the head bearing on the lip rather than the conical seat. For the full breakdown of CSK angles, drive styles, machine screws vs wood screws vs Tek screws vs rivets vs concrete anchors, and how to cut the countersink hole correctly, see our dedicated Countersunk Screw Guide. Raised Countersunk (Oval) Head — Decorative Flush The raised countersunk head — also called oval head, particularly in cabinet and joinery contexts — has the same conical underside as a standard CSK screw but with a small domed top that sits proud of the surface when fully driven. It combines the flush-fit clamping of a CSK with a finished decorative profile. Where raised CSK is used Cabinet hardware — handles, hinges, drawer slides where the proud dome is part of the visual design. Decorative joinery — visible fasteners on furniture, where a flat CSK looks too utilitarian. Door and window furniture — escutcheons, plates, lock cylinders. Period architecture restoration — historical fixtures often called for raised CSK as standard. Stock at AIMS is most commonly slotted or Phillips drive, in brass, zinc-plated steel, and 304/316 stainless for marine and outdoor work. Less commonly stocked than flat CSK but readily orderable. Dome / Round Head — Decorative and Historical The dome head (sometimes called round head in older references) has a tall hemispherical or partial-spherical top with a flat underside. It is more decorative than a button head and considerably taller. The bearing area is narrower than a pan head — closer to a button head — and the head sits noticeably proud. Dome heads are not a common modern industrial fastener. They appear in: Electrical terminals and binding posts — particularly older British-spec hardware where the slotted dome head was the default. Decorative ironwork and architectural metalwork — visible fasteners on gates, railings, period cabinetry. Restoration work — replacing original-era fasteners on heritage equipment, vehicles, or buildings. Some carriage / coach bolt applications — though these are technically a different fastener (see our Hex Bolt Guide). For most modern industrial applications, a button head delivers the same decorative effect with less head height, better drive engagement, and easier installation. Cheese & Fillister Heads — Cylindrical Machine Screws The cheese head is a cylindrical head with a flat top and rounded edges where the cylinder meets the underside. It is taller and narrower than a pan head — more like a short cylinder than a low dome. In the original British engineering tradition (BSW/BSF), the cheese head was the standard machine screw head profile. The fillister head is closely related: cylindrical like a cheese head, but with a more pronounced rounded top instead of a flat one. The two terms are sometimes used interchangeably, but on engineering drawings: Cheese head — flat top, vertical cylindrical sides. Fillister head — slightly domed top, cylindrical sides. Both are uncommon in modern Australian trade work — pan heads have replaced them in most general applications. They still appear in older British-spec equipment, instrumentation, scientific apparatus, and any place where a tall narrow head profile is intentional (e.g. to clear an adjacent component while leaving the drive accessible). If you encounter "cheese" or "fillister" on a parts list and cannot source the exact part, a pan head will usually substitute — but check the head height clearance first. Bugle, Wafer & Hex Flange — Specialty Heads Bugle head — drywall and decking The bugle head is a special variant of the countersunk head where the underside is curved rather than straight-conical. The curve transitions smoothly from the shank into the head, allowing the screw to self-countersink in soft materials — gypsum board, MDF, soft timber — without splitting or tearing. The curved underside crushes the soft material gradually rather than wedging it apart. Bugle heads are the standard for: Drywall / plasterboard screws — the curve compresses the gypsum without tearing the paper face. Deck screws — sets cleanly in softwood without pre-drilling, leaves a flush finish. MDF and chipboard fastening — particle materials where a CSK would split the surface. Cement-fibre sheet (e.g. Hardie) — specialty bugle-head Tek screws for fibre cement cladding. Drive is most commonly Phillips, Pozi, square (Robertson), or Torx. The square drive is particularly popular for deck screws because it allows single-handed bit-on-screw placement at angle. Wafer head — metal framing and Tek screws The wafer head is a very flat, slightly domed head — flatter than a truss head, broader than a pan head. It is the standard for self-drilling Tek-style screws used in light steel framing, ducting, and sheet-to-frame metal work. The low profile minimises head height proud of the sheet, while the wide bearing surface prevents pull-through in 0.5 mm to 1.5 mm steel. If you are working with metal framing or thin steel sheet, wafer head Tek screws (to AS 3566) are typically the first choice. See our Self-Tapping & Self-Drilling Screws Guide for the full Tek screw breakdown including gauge, drilling capacity, and substrate selection. Hex flange head — high-torque with built-in washer A hex flange head combines a standard external hex (six-flat) with an integrated flanged underside — effectively a hex bolt with a built-in washer. The flange spreads clamping load across a wider area than a plain hex head, reducing pull-through and removing the need for a separate flat washer in many applications. Used widely in: Automotive and machinery — engine accessories, transmission housings, vibration-prone joints. Sheet metal and ducting — combines truss-head bearing area with hex-driven torque capability. Production assembly — eliminates the washer step on the line. For full external-hex fastener selection, see our Hex Bolt Guide. Security & Tamper-Resistant Heads Security screw heads are designed to be installed with a regular tool but resist removal — a deterrent against vandalism, theft, unauthorised disassembly, or accidental dismantling. AIMS stocks the full security fastener range, and we are also the AU supplier of the Champion OWS-RT One-Way Screw Removal Tool — the standard kit for taking out security screws when authorised access is needed. The main security head types Type How it works Typical use One-way (clutch head) Slotted-style head with sloped flanks — installs with a flathead driver, but the flanks slip past the driver in the reverse direction. Cannot be unscrewed with any standard driver. Public toilet partitions, security panels, retail fittings, vehicle plates Spanner head (snake-eye / pig-nose) Two pin holes drilled into the head face. Requires a matching two-pin spanner driver. Public infrastructure, switchgear panels, security cabinets Pin-in-Torx (T-pin) Standard Torx recess with a centre pin. Standard Torx bit will not fit; requires a pin-in-Torx bit with a corresponding centre hole. Electronics enclosures, school lab equipment, public terminals Pin-in-hex (T-pin Allen) Hex socket with a centre pin. Standard Allen key will not fit; requires a pin-in-hex bit. Public seating, waste bins, signage, security fixtures Tri-wing / tri-groove Three- or six-point asymmetric recess. Requires a specific proprietary driver. Aerospace, electronics, military, gaming hardware Breakaway / shear-off Hex head with a shear groove. Tighten until the outer head shears off, leaving a smooth shank that cannot be gripped. Permanent installations, security plates, anti-theft mounting Removing security screws — the Champion OWS-RT The most common security head AIMS sees in the field is the one-way (clutch) head, used in commercial bathrooms, retail security fittings, signage, vehicle number plates, and similar high-vandalism applications. Once installed, it cannot be removed with any standard driver — the flanks of the slot deflect the bit out under reverse torque. The Champion OWS-RT One-Way Screw Removal Tool is the AU standard for authorised removal. It is a hardened-tip set that grips the one-way head profile from above — the tip bites into the slope, allowing reverse torque to be applied without slipping. Used by: Locksmiths and security technicians Maintenance trades on public infrastructure Vehicle workshops removing tamper-evident plates Anyone replacing or servicing fixtures originally installed with one-way screws Specify the OWS-RT alongside any one-way / clutch-head security screw order — it is the only practical removal solution for this head type. Choosing by Application — Selection Table Map common AU industrial scenarios to the right head type: Application Recommended head Why Sheet metal fastening (0.5–1.5 mm steel) Wafer or truss head Wide bearing area prevents pull-through Light steel framing (20-gauge) Wafer head Tek (AS 3566) Self-drilling + wide bearing Drywall / plasterboard Bugle head Self-countersinks without tearing paper Decking Bugle head, square or Torx drive Self-countersinks, holds tight in softwood Hinges, brackets, structural fittings Countersunk (CSK) Flush mount, snag-free, shear-resistant Cabinet hardware (visible) Raised countersunk (oval head) Flush clamp + decorative dome Engineered machine joints (high-torque) Cap head (DIN 912) Class 12.9 standard, deep socket Light fastening with cosmetic finish Button head Low-profile rounded, decorative Electrical control panels Pan head, Phillips drive Standard, well-stocked, drive-tool universal Structural steel through-bolting Hex head bolt External drive, full spanner/socket access Public bathroom partitions / anti-theft One-way (security) head Cannot be removed without OWS-RT tool Concealed structural fixings Cap head in counterbore Fully recessed, maximum strength Soft timber / MDF / chipboard Bugle head Self-countersinks without splitting Marine / coastal exposure Any head, 316 stainless Material matters more than head shape — choose head by job, then specify 316 Three quick decision rules: (1) Need flush mounting? Countersunk, bugle, or counterbored cap head — that's it. (2) Worried about pull-through in thin sheet or soft material? Truss, wafer, or bugle. (3) High-torque engineered joint? Cap head (Class 12.9) or hex head — never button or truss. Australian Terminology & Stock Notes Three things worth knowing about AU fastener language and supply: "Flat head" is ambiguous In fastener supply, "flat head" almost always means countersunk (CSK) — the screw with a flat-topped conical underside that sits flush. In tool supply, "flat head" can mean a slotted screwdriver tip. When ordering, specify "countersunk" or "CSK" to avoid confusion. When discussing on the floor, the context usually makes it clear — but on a written parts list, ambiguity costs time. "Truss head" / "mushroom head" / "oven head" All three names refer to the same wide-bearing, low-profile dome shape. In Australian product catalogues "truss" is the standard term. "Mushroom" appears in some fabrication trades. "Oven head" is rare in AU and more common in older US engineering literature. If a parts list calls for any of these three, you are looking for the same head shape. AS standards relevant to head types AS 3566 — Self-drilling screws (wafer head Tek-style screws for metal framing). AS/NZS 1390 — Cup head bolts (the Australian carriage / coach bolt standard). AS/NZS 4680 — Hot-dip galvanised fasteners (applies across all head types). ISO 7380 / DIN 7380 — Button head socket screws. ISO 4762 / DIN 912 — Cap head socket cap screws (covered in the Socket Head Cap Screw Guide). ISO 10642 / DIN 7991 — Countersunk socket screws. DIN 7985 — Pan head Phillips machine screws. AIMS stock summary AIMS Industrial holds the full common-head metric range across grades 4.6 / 8.8 / 10.9 / 12.9 carbon steel and A2 (304) / A4 (316) stainless: Pan head screws — full metric range, multiple drives, multiple materials Button head socket screws — DIN 7380 metric, Class 10.9 / 12.9 / stainless Socket head cap screws — DIN 912 (see Art 125) Countersunk machine screws — multiple drives, multiple materials Tek / self-drilling screws — wafer, hex flange, bugle (see Art 19) Hex bolts and hex flange bolts (see Art 55) Security screws and the Champion OWS-RT removal tool For the matching nuts and washers across all these head types, see our Types of Nuts Guide and Types of Washers Guide. For hand-tightened applications, the nut-side companion to this guide is our Wing Nut Guide. For fastener strength and grade selection across all head types, see the Bolt Grade Chart. If a screw head is rounded, cammed-out, or snapped flush, work through the recovery options in our How to Remove Stuck Bolts & Nuts guide — penetrant, impact, extractors, drill-out and weld-on, with stripped-head specifics. For the broader fastener orientation — thread systems, property classes, head/drive/nut/washer types and selection rules — see our Fastener Quick Guide. Frequently Asked Questions What are the most common types of screw heads? The seven most common screw head shapes in Australian industrial supply are pan head, button head, truss head, countersunk (flat / CSK), raised countersunk (oval), dome (round), and hex head. Cap head (DIN 912 socket head cap screws) is also extremely common in engineered joints. Specialty heads include bugle (drywall / decking), wafer (metal framing), hex flange (high-torque with built-in washer), and a range of security heads (one-way, spanner, pin-in-Torx, pin-in-hex). What's the difference between a pan head and a button head screw? A pan head has a flat top, slightly rounded edges, and is generally driven with a Phillips, Pozi, Torx, or slotted recess. A button head has a low rounded dome top with a hex socket (Allen) or Torx drive, and a smaller diameter than an equivalent pan head. Pan heads have a deeper drive recess, allowing more torque before stripping; button heads have a lower profile and a more decorative finish but approximately 30–40% lower torque rating than equivalent socket cap heads. What's the difference between a pan head and a truss head screw? A truss head is much wider and lower-profile than a pan head — designed to spread clamping load across a larger bearing area. The wider underside is ideal for thin sheet metal, soft materials, or any application where pull-through is a concern. The trade-off is torque: truss heads are thinner than pan heads and have a lower torque rating before the head shears or the drive strips. Use truss for bearing area; use pan for general fastening with higher drive torque. What is a truss head screw used for? Truss head screws are used wherever a wide bearing area and low head profile matter more than maximum drive torque. The most common applications are sheet metal fastening, light steel framing (20-gauge studs and tracks), ducting, soft timber and plastic, and large-format panel attachment. The wide head distributes clamping force, dramatically reducing the chance of dimpling, tearing, or pulling through thin or soft material. Truss heads are sometimes called mushroom head or oven head — all three terms refer to the same shape. What is a countersunk screw used for? Countersunk (CSK) screws are used wherever the head must sit flush with — or below — the surface of the workpiece. The conical underside of the head matches a tapered countersunk hole in the material, distributing clamping load radially outward. Standard applications include hinges, machinery guards, structural steel connections, handrails, kitchen and cabinet hardware, and any surface where a protruding head would be a snag hazard, clearance problem, or cosmetic issue. See our dedicated countersunk screw guide for full angle (90° vs 82°), type, and drilling guidance. What is the difference between a flat head and a countersunk screw? In fastener language, "flat head" and "countersunk" are usually the same thing — a screw with a conical underside and a flat top that sits flush with the work surface. The term "flat head" is more common in North American usage; "countersunk" or "CSK" is the standard Australian and British term. Confusion can arise because in tool supply "flat head" sometimes means a slotted screwdriver tip — when ordering screws, specify "countersunk" or "CSK" to remove ambiguity. What is a bugle head screw used for? Bugle head screws are designed for self-countersinking in soft materials. The underside of the head curves smoothly from the shank, allowing the screw to compress and sink into materials like gypsum drywall, MDF, chipboard, fibre cement sheet, and soft timber without splitting, tearing, or requiring a pre-drilled countersink. The standard applications are drywall screws, deck screws, MDF fastening, and Hardie or other cement-fibre cladding screws. Drive style is most commonly Phillips, Pozi, square (Robertson), or Torx. What head type is best for sheet metal? For thin sheet metal (0.5 mm to 1.5 mm steel) and metal framing, the best head types are wafer head and truss head — both have a wide, flat bearing surface that distributes clamping load and prevents the head from pulling through the sheet. Wafer head is the standard for AS 3566 self-drilling Tek screws used in light steel framing and ducting. Truss head is preferred where maximum bearing area is needed. Avoid pan heads in thin sheet — the smaller bearing surface concentrates load and can dimple or tear the metal. What is a wafer head screw? A wafer head is a very flat, slightly domed screw head — flatter than a truss head and broader than a pan head. It is the standard for self-drilling Tek-style screws used in light steel framing, ducting, and sheet-to-frame metal fastening to AS 3566. The low profile keeps the head close to the surface; the wide bearing area distributes clamping force and prevents pull-through in thin steel sheet. Wafer-head Tek screws are typically supplied with a Phillips, Pozi, or hex socket drive. What is the difference between a screw head and a screw drive? The head is the shape of the fastener at the top of the shank — pan, button, truss, countersunk, dome, hex, and so on. The drive is the recess (or external profile) the bit engages — Phillips, Pozi, Torx, hex socket, slotted, square (Robertson), and others. Head shape and drive style are independent decisions: a pan head can come with Phillips, Pozi, Torx, or slotted drive; a cap head almost always uses hex socket; a hex bolt uses an external hex driven by a spanner. See our screwdriver types guide for the full drive recess breakdown. Are pan head and button head screws interchangeable? Generally yes for light fastening, with two cautions. First, button heads have approximately 30–40% lower torque rating than the equivalent socket cap head and somewhat lower torque rating than a pan head with a deeper drive recess — over-torquing a button head strips the socket. Second, the head profiles are visibly different: button heads are rounded and decorative; pan heads are flatter and more utilitarian. For high-torque engineered joints, do not substitute a button head for a pan or cap head without checking the joint design. For light decorative fastening, the swap is usually fine. What is a security screw head? A security screw head is designed to be installed with a standard or specialist tool but resist removal — a deterrent against vandalism, theft, or unauthorised disassembly. Common types include one-way (clutch) heads, spanner head (snake-eye / pig-nose), pin-in-Torx, pin-in-hex, tri-wing, and breakaway / shear-off heads. The most common in Australian commercial use is the one-way head, found in public bathrooms, retail security fittings, vehicle plates, and signage. Authorised removal of one-way screws requires a specialist tool — the Champion OWS-RT One-Way Screw Removal Tool is the standard kit available at AIMS Industrial. How do I remove a one-way / security screw? One-way (clutch) screws are designed so that the slope of the head deflects a standard driver out under reverse torque — they cannot be unscrewed with a flathead, Phillips, or any conventional bit. The standard authorised removal solution is the Champion OWS-RT One-Way Screw Removal Tool, which has hardened tips that grip the head profile from above and apply reverse torque without slipping. The OWS-RT is the AU industry standard for locksmiths, security technicians, and trades servicing public infrastructure or fixtures originally installed with one-way screws. For other security types (pin-in-Torx, pin-in-hex, tri-wing, spanner head), specific matching driver bits are required — these are also available at AIMS Industrial. Can I substitute one head type for another in the same application? Sometimes, but never assume. The head dictates how the screw seats, how the load is transferred, and what tool drives it. You can usually substitute pan ↔ button heads in light decorative fastening; you can usually substitute truss ↔ wafer for sheet metal work. You cannot substitute a pan head for a countersunk screw — the pan head will not sit flush in a countersunk hole. You cannot substitute a button head for a cap head in a high-torque joint — the button head will strip before achieving full clamping force. When in doubt, match the original specification, and if the original specification is unknown, choose by application using the selection table in this guide. Are screw head types standardised in Australia? Australian fastener supply uses ISO and DIN metric standards for almost all head types — DIN 7985 (pan head Phillips), DIN 7991 / ISO 10642 (countersunk socket), DIN 7380 / ISO 7380 (button head socket), DIN 912 / ISO 4762 (cap head socket), and so on. AS-specific standards exist for self-drilling screws (AS 3566) and cup head bolts (AS/NZS 1390), and AS/NZS 4680 governs hot-dip galvanised finish across all head types. Imperial UNC / UNF heads (with their distinct angle and dimension specifications) appear on legacy and imported equipment but are not the standard for new AU industrial work. When ordering, specify the standard (e.g. "DIN 7991 M8 × 30 CSK socket Class 12.9") for unambiguous supply. For a full breakdown of metric and imperial thread standards used in Australian industry — including UNC, UNF, BSW and BSF — see the AIMS metric vs imperial fasteners guide. Pair this guide with our Spanner Size Chart for matching the spanner across-flats dimension to the bolt head. The matching socket and drive size live in our Socket Size Chart — every common fastener head covered. People Also Ask — Screw Head Types Q: What is the difference between a countersunk and a pan head screw? A countersunk (also called flat head or CSK) screw has an angled conical underhead that sits flush with or below the material surface when installed in a matching countersunk hole. A pan head screw has a flat top with a rounded edge and a flat bearing surface underneath, sitting proud of the material surface. Countersunk screws are used where a flush finish is required; pan heads are used where a raised head is acceptable and provides more bearing area. Q: What drive type is best for high-torque applications? Torx (star drive) and square (Robertson) drives are superior for high-torque applications because they allow the driver to push straight down without cam-out risk. Phillips and Pozidriv drives are designed to cam out at a set torque, which reduces over-tightening but limits maximum torque. Internal hex (Allen/cap head) also handles high torque well. For power tool assembly lines and structural fastening, Torx is widely preferred for consistent torque transfer. Q: What is the difference between Phillips and Pozidriv screws? Both have a cross-shaped recess but differ in design details that make them incompatible. Phillips has tapered flanks designed to allow the driver to cam out under excessive torque. Pozidriv has additional tick marks between the cross arms and straight (not tapered) drive walls, providing much better driver engagement and substantially reducing cam-out. Using a Phillips driver in a Pozidriv screw — or vice versa — damages the recess quickly. Q: What does CSK mean on a screw? CSK stands for countersunk. A CSK screw has an angled conical head, typically at 82° or 90° included angle, designed to sit flush with or below the surface of the work piece when driven into a matching countersunk hole. The angle of the countersink in the workpiece must match the angle of the screw head. Most metric CSK screws use a 90° included angle; some imperial and woodworking applications use 82°. Q: When should I use a dome or round head screw instead of a flat head? Dome (mushroom) or round head screws are used when a flush finish is not required and a decorative or finished appearance is desired — common in furniture, architectural joinery, and electronics. They provide a larger bearing surface than flat heads. They cannot be used where the fastener must sit flush with or below the surface. Dome heads are also commonly used in sheet metal applications where a large bearing area prevents the screw from pulling through thin material.
Read moreSocket Head Cap Screw Guide: DIN 912, Grades, Sizes & Allen Key Selection
Bookmark our Engineering Reference Charts hub for related sizing tables, conversion charts and Australian standard references across 9 topic clusters. Cap Head, Button Head, Flat (Countersunk) Head — Types Compared — Quick Reference "Socket head cap screw" technically refers to the standard cylindrical-head DIN 912 fastener. In broader trade language, "socket screw" can mean any screw with a hex socket drive, which includes button-head and countersunk variants. Type Standard Profile Torque vs Cap Head Best For Cap head (SHCS) DIN 912 / ISO 4762 Tall cylindrical head, deep socket 100% (reference) Engineered joints, high-strength applications, counterbored holes Button head (BHCS) DIN 7380 / ISO 7380 Low-profile rounded head, shallow socket ≈ 60–70% Tight clearance, cosmetic finish, light-to-medium loading Flat / countersunk (FHCS) DIN 7991 / ISO 10642 Conical 90° head, shallow socket ≈ 50–60% Flush-fit applications, no protruding head, hinges and brackets Low head DIN 6912 Reduced-height cylindrical head, shallow socket ≈ 70–80% Tight clearance where DIN 912 won't fit, lower-torque applications Shoulder bolt ISO 7379 Cap head + precision-ground unthreaded shoulder Variable (load-bearing shoulder, not the thread) Pivots, dowel pins, jig location bolts, stripper bolts in dies What Is a Socket Head Cap Screw? A socket head cap screw is a high-strength precision fastener with a cylindrical head and an internal hex (Allen) socket drive. It is the workhorse fastener of machine design, used wherever an engineer needs a compact head profile, predictable clamping force, and the option to sit fully recessed below a finished surface in a counterbored hole. For the full metric bolt range across all head profiles — hex head, button head, countersunk, set screws, M3 through M24 — see the AIMS Metric Bolt Size Guide for diameter, thread pitch and head dimension references. The name describes the geometry exactly. The head is a plain cylinder, slightly larger in diameter than the threaded shank. The socket is a hexagonal recess machined into the top of the head, driven by a hex (Allen) key from above rather than by a spanner from the side. The cap reference is historical — early machine builders called these "cap screws" because they sat as a cap on top of the joint. The shank below the head is fully or partially threaded, depending on the length and grip required. In Australian workshops you will hear them called by several names — all referring to the same fastener: Allen bolt — the most common AU trade term, after the Allen Manufacturing Company that popularised the hex socket drive in the early 1900s. Cap screw or cap head screw — short form, used on parts lists and stock cards. Allen head screw or Allen key bolt — verbal terms used on the floor. Socket bolt or hex socket bolt — used in engineering drawings. SHCS — abbreviation that appears on parts lists and stock-keeping systems. DIN 912 — used as a stand-alone descriptor in engineering specifications. If a maintenance fitter asks for "an Allen bolt", they are asking for a socket head cap screw. If a technical drawing calls out "M10 × 50 SHCS Class 12.9", that is also a socket head cap screw. Always confirm thread size, length, grade, and material when ordering — the term alone does not specify the part. Quick reference: Socket head cap screw = Allen bolt = cap screw = DIN 912 = ISO 4762. All the same fastener, different names depending on whether you are reading a spec sheet or talking to the fitter on the floor. How to Measure a Socket Head Cap Screw To order or specify a socket head cap screw correctly you need five dimensions. Get any one of them wrong and the screw will not fit, will not clamp correctly, or will fail in service. Thread diameter (nominal size) — the major diameter of the thread, expressed in millimetres for metric screws (M3, M4, M5, M6, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30 and larger). Most AU socket head cap screws are metric. Imperial sizes (1/4", 5/16", 3/8", 1/2") are still encountered on imported American machinery and some agricultural equipment. Thread pitch — the distance between thread crests, in millimetres. DIN 912 socket head cap screws are supplied with coarse pitch as standard (e.g. M8 × 1.25, M10 × 1.5, M12 × 1.75). Fine-pitch versions exist for high-vibration or precision applications and must be specified explicitly. Length — measured from under the head to the end of the thread. The head is not included in the length measurement, because the head sits above (or recessed into) the workpiece while the threaded portion enters the joint. Common stock lengths for an M8 cap screw are 16, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120 and longer. Head diameter — the outside diameter of the cylindrical head. This dimension is fixed by DIN 912 for each thread size and matters when the head must clear into a counterbored hole or sit within a recess. Example: an M8 cap screw has a 13 mm head diameter and 8 mm head height. Hex socket size (across flats) — the size of the Allen key required to drive the screw, measured across the flat sides of the hexagonal recess. This is also fixed by DIN 912 and varies by thread size. M8 takes a 6 mm hex key; M10 takes 8 mm; M12 takes 10 mm. The full table appears later in this guide. The standard way to specify a socket head cap screw on a parts list is: M[size] × [length] SHCS, Class [grade], [material/finish]. For example: "M10 × 40 SHCS, Class 12.9, black oxide" — that is unambiguous and orderable from any AU industrial supplier. The DIN 912 / ISO 4762 Standard Two standards govern socket head cap screw dimensions. They are dimensionally compatible — a screw made to DIN 912 will fit the same hole and use the same Allen key as one made to ISO 4762 — but you will see both labels in AU supply. DIN 912 is the German national standard, first published in 1936. For decades it was the global default for socket head cap screws, and most AU distributors still label stock "DIN 912" simply because that is how the manufacturer marks the box. ISO 4762 is the international successor, first published in 1989 and updated several times since. ISO replaced DIN as the official global standard, and modern engineering drawings tend to specify ISO 4762 for new designs. The two standards specify identical head dimensions, hex socket sizes, and thread tolerances for sizes M3 through M64. The only practical difference is the documentation — and even that is converging as DIN 912 is now harmonised with ISO 4762. What both standards define for each thread size: Head diameter (cylinder OD) Head height Hex socket size (across flats) Hex socket depth Thread length and run-out Property classes (8.8, 10.9, 12.9 for steel; A2-70, A4-70, etc. for stainless) Surface finish requirements What neither standard mandates is torque — torque values are derived from the property class, thread size, friction coefficient, and joint geometry. We provide an indicative torque table further down this guide, but always check the equipment manual for the specific torque your application requires. Warning — DIN 912 vs DIN 6912: Do not confuse DIN 912 with DIN 6912. DIN 6912 is a low-head variant — same thread but with a noticeably shorter head and shallower socket. Useful for tight clearances but rated for significantly less torque than DIN 912. Always check the carton if you receive a delivery that looks "different" — the difference is real and the screws are not interchangeable. Cap Head, Button Head, Flat (Countersunk) Head — Types Compared "Socket head cap screw" technically refers to the standard cylindrical-head DIN 912 fastener. In broader trade language, "socket screw" can mean any screw with a hex socket drive, which includes button-head and countersunk variants. Knowing the difference matters because the head profile changes the strength, the bearing surface, and the type of hole you need to prepare. For a wider comparison covering pan, truss, dome, wafer, bugle and other head shapes beyond the socket-driven family, see our Screw Head Types Guide. Type Standard Profile Torque vs Cap Head Best For Cap head (SHCS) DIN 912 / ISO 4762 Tall cylindrical head, deep socket 100% (reference) Engineered joints, high-strength applications, counterbored holes Button head (BHCS) DIN 7380 / ISO 7380 Low-profile rounded head, shallow socket ≈ 60–70% Tight clearance, cosmetic finish, light-to-medium loading Flat / countersunk (FHCS) DIN 7991 / ISO 10642 Conical 90° head, shallow socket ≈ 50–60% Flush-fit applications, no protruding head, hinges and brackets Low head DIN 6912 Reduced-height cylindrical head, shallow socket ≈ 70–80% Tight clearance where DIN 912 won't fit, lower-torque applications Shoulder bolt ISO 7379 Cap head + precision-ground unthreaded shoulder Variable (load-bearing shoulder, not the thread) Pivots, dowel pins, jig location bolts, stripper bolts in dies The reason cap head outperforms the others on torque is the depth of the hex socket. The deeper the socket, the more contact area between the Allen key and the head walls, and the more torque can be applied without rounding the recess. A button head's socket is typically half the depth of a cap head's, which is why a stripped button head is one of the most common failures on lighter machinery. For the dedicated button head deep-dive — ISO 7380-1 vs 7380-2 flanged, sizes, torque limits and the engineering reasons not to substitute — see our Button Head Socket Screw Guide. For maximum-strength engineered joints — drives, dies, gearbox covers, structural fixings on vibrating equipment — specify cap head. For appearance-grade applications, light enclosures, or where the head must clear above a panel, button head is appropriate. For flush-fit work, see our Countersunk Screw Guide. Grades and Strength: 8.8, 10.9 and 12.9 Explained Steel socket head cap screws are sold by property class — a two-part number (8.8, 10.9, 12.9) that is far more useful than the historical "high tensile" or "low tensile" labels. Each part of the number tells you something specific. The first number (before the decimal) is approximately the ultimate tensile strength in units of 100 MPa. So Class 8.8 has roughly 800 MPa tensile strength; Class 12.9 has roughly 1220 MPa. The second number (after the decimal) is the ratio of yield strength to ultimate tensile strength, multiplied by 10. So Class 8.8 has yield = 0.8 × 800 = 640 MPa. Class 12.9 has yield = 0.9 × 1220 ≈ 1100 MPa. Property class Tensile strength (MPa) Yield strength (MPa) Hardness (HRC) Common usage Class 8.8 800 min. 640 min. 22–32 General industrial, machine guards, brackets, lower-stress fasteners Class 10.9 1040 min. 940 min. 32–39 Structural machine joints, gearbox covers, mid-range engineered fasteners Class 12.9 1220 min. 1100 min. 39–44 Standard grade for SHCS — dies, jigs, drives, high-strength engineered joints Class 14.9 1400 min. 1260 min. 44–48 Specialised applications — aerospace, motorsport, ultra-high-strength joints The single most important thing to know about socket head cap screws is that Class 12.9 is the engineering default. When a designer specifies "M10 × 40 SHCS" without giving a grade, they almost always mean 12.9. The very design of the cap screw — narrow head, deep socket, used in tight machined joints — assumes a high-strength grade. If you replace a 12.9 with an 8.8, you have reduced clamping force by roughly 40%, which can fatigue the joint, allow vibration loosening, and ultimately fail. For a complete breakdown of grade markings, head identification, and full mechanical properties for all bolt grades, see our Bolt Grade Chart. Warning — substituting grades: Never replace a Class 12.9 cap screw with a Class 8.8 unless the joint has been re-engineered. The original torque, preload, and joint stiffness calculations were done for the higher grade. Lower-grade replacement looks the same on the shelf but will yield, stretch, or fatigue in service. If 8.8 is the only grade available, downgrade the torque to match — or get the right grade. Material Selection: Steel, Stainless and Bumax Socket head cap screws come in five common materials at AIMS Industrial. Each has a defined application range and a defined limit. The fastener carton always lists the material — never assume; always read. Class 12.9 Black Oxide Carbon Steel The default. Carbon steel heat-treated to Class 12.9, with a black oxide finish that provides mild corrosion resistance and a distinctive matte black appearance. Used for indoor industrial applications: machine bases, gearbox covers, dies, jigs, fixtures, and any precision-engineered joint where the Class 12.9 strength is required and the environment is dry. The black oxide is not a long-term corrosion barrier — for outdoor or wet exposure, choose zinc-plated or stainless. Class 8.8 / 10.9 Zinc-Plated Carbon Steel Carbon steel with electroplated zinc finish (typically 5–8 microns), often passivated for an extra layer of corrosion resistance. Lower strength than 12.9 — typically supplied as Class 8.8 or 10.9. Suitable for indoor and light outdoor industrial applications where corrosion exposure is moderate. The zinc plating is decorative-grade only — for genuine outdoor exposure, hot-dip galvanised or stainless is required. 304 (A2-70) Stainless Steel The standard stainless grade for general industrial work. Property Class A2-70 — approximate tensile strength 700 MPa, yield around 450 MPa. Roughly equivalent to a Class 8.8 carbon steel screw in tensile, but somewhat weaker in yield. Suitable for food processing (non-chloride), light marine (sheltered), pharmaceutical, and most outdoor applications away from salt water. Excellent corrosion resistance to fresh water, mild acids, and atmospheric moisture. 316 (A4-70) Stainless Steel Adds molybdenum to the 304 chemistry, which provides resistance to chloride attack. Property Class A4-70 — similar mechanical properties to 304 but considerably better corrosion resistance in salt water, chlorinated water, food processing brines, and chemical environments. Specify 316 for: marine work (boats, jetties, coastal infrastructure), chlorinated swimming pools, pickling baths, food processing with brine, and any AU coastal industrial site within roughly 1 km of the surf. Cost is around 30% above 304. Bumax 88 / Bumax 109 — High-Strength Stainless A specialty stainless grade developed for applications that need both 12.9-equivalent strength and the corrosion resistance of stainless. Bumax 88 has tensile strength around 800 MPa (Class 8.8 equivalent in strength but in stainless); Bumax 109 has tensile strength around 1000 MPa (close to Class 10.9 in strength). Used in oil and gas, defence, subsea infrastructure, motorsport, and high-end food processing where standard 316 lacks the strength but mild steel cannot survive the environment. Available at AIMS Industrial for specification work. Warning — stainless is not a 12.9 substitute: Standard 304 or 316 stainless socket head cap screws are property class A2-70 or A4-70 — roughly equivalent to Class 8.8 in tensile strength, not Class 12.9. Replacing a Class 12.9 cap screw with stainless reduces clamping capacity by approximately 40%. If you need stainless corrosion resistance with high-grade strength, specify Bumax. Do not assume "stainless = strong". Stainless and galling — the silent failure The most common failure mode of stainless socket head cap screws is not corrosion or overload — it is galling. When stainless threads are tightened without lubricant, the soft, ductile thread surfaces cold-weld together as friction heats them. The threads seize irreversibly. The screw cannot be removed without drilling out, and often cannot be tightened to specification because the galling occurs partway through the torque. The fix is simple: always apply a thread lubricant or anti-seize compound to stainless threads before installation. Nickel-based or moly-based anti-seize is the industrial default. PTFE thread paste also works for lower-torque applications. Never install a stainless cap screw dry into a stainless thread. Socket Head vs Hex Head: Which to Choose The choice between a socket head cap screw and a hex bolt usually comes down to one factor: clearance. A hex bolt is driven by a spanner or socket from the side. The spanner needs swing room — typically a clearance arc of around 60° for a ratchet — and the bolt head sits proud of the work surface. Where there is space and where a quick-release joint matters (vehicle wheels, building structural connections, exposed brackets), the hex bolt is the right choice. A socket head cap screw is driven by an Allen key from above. It needs no side clearance — only a clear path down the centreline of the screw. The head can sit fully recessed in a counterbored hole, completely below the surface of the part. This makes the SHCS the only practical choice for: Counterbored holes — gearbox covers, machinery enclosures, motor mounts Recessed mounting — die plates, fixture plates, jig bases Tight clearances — where a hex spanner would not fit between adjacent components Machined assemblies — where surface continuity matters High-strength precision joints — where Class 12.9 is required and a hex bolt of equivalent grade is unavailable The other practical difference is grade availability. Hex bolts are most commonly stocked in Class 8.8 or 10.9; Class 12.9 hex bolts are uncommon and often special-order. Socket head cap screws are stocked in Class 12.9 as the default. If your design calls for 12.9 strength, the SHCS will almost always be more readily available. Decision factor Hex bolt Socket head cap screw Side clearance for spanner Required Not required Above-head clearance for driver Optional Required (Allen key) Counterbored / flush installation Not possible Standard application Common stock grades 4.6, 8.8, 10.9 8.8, 10.9, 12.9 standard Driver tool Spanner / socket Hex (Allen) key Quick removal under field conditions Faster Slower (Allen key engagement) Cost (same grade, same size) Lower Slightly higher For full hex bolt selection guidance, head markings and grade chart, see our Hex Bolt Guide. Hex Key (Allen Key) Sizes for Metric Socket Head Cap Screws The single most useful piece of information when working with socket head cap screws is the hex key size — and it is not obvious from the screw's thread size alone. The DIN 912 standard fixes the hex socket size for each thread, so once you know the table, you know the key. Use the wrong size and you will round out the socket. Thread size Hex key (across flats) Head diameter Head height M3 2.5 mm 5.5 mm 3.0 mm M4 3 mm 7.0 mm 4.0 mm M5 4 mm 8.5 mm 5.0 mm M6 5 mm 10.0 mm 6.0 mm M8 6 mm 13.0 mm 8.0 mm M10 8 mm 16.0 mm 10.0 mm M12 10 mm 18.0 mm 12.0 mm M14 12 mm 21.0 mm 14.0 mm M16 14 mm 24.0 mm 16.0 mm M18 14 mm 27.0 mm 18.0 mm M20 17 mm 30.0 mm 20.0 mm M22 17 mm 33.0 mm 22.0 mm M24 19 mm 36.0 mm 24.0 mm M27 19 mm 40.0 mm 27.0 mm M30 22 mm 45.0 mm 30.0 mm M36 27 mm 54.0 mm 36.0 mm Two practical points the table will not tell you: Imperial sizes use a different table. An imperial 1/4" socket head cap screw takes a 3/16" hex key — not a metric key of any size. Mixing metric and imperial drivers is one of the fastest ways to round out a socket. If the screw came off American machinery, assume imperial until proven otherwise. Worn keys round out sockets. A used long-arm hex key with a slightly bevelled tip will fit looser than a new one. The looser fit means the corners contact, not the flats — and the corners shear off the socket walls before they shear off the harder hex key. Replace bent or rounded keys before they damage your screws. For a complete guide to Allen keys, including ball-end vs flat tip, T-handle vs L-handle, torque ratings, and how to choose a hex key set, see our Allen Key & Hex Key Guide. Torque Values for Metric Socket Head Cap Screws Torque is what converts a screw into a clamping force. Too little torque and the joint loosens under vibration. Too much torque and the screw yields, stretches, or snaps. The torque required is determined by the screw's grade, thread size, friction coefficient (lubricated vs dry), and the joint geometry. The values in the table below are indicative dry-thread torques for general industrial use. They assume clean, dry threads with no lubricant or anti-seize. Reduce by approximately 15–20% if threads are oiled, or by 25% if anti-seize compound is applied. Always defer to the equipment manufacturer's specified torque if one is given — these table values are a default, not a substitute for engineering data. Thread size Class 8.8 (Nm) Class 10.9 (Nm) Class 12.9 (Nm) M3 1.3 1.8 2.2 M4 3.0 4.4 5.1 M5 6.0 8.7 10.2 M6 10.4 15.0 17.5 M8 25.0 36.0 43.0 M10 49.0 72.0 84.0 M12 86.0 125.0 145.0 M14 135.0 200.0 235.0 M16 210.0 310.0 365.0 M18 290.0 430.0 500.0 M20 410.0 610.0 710.0 M22 560.0 825.0 970.0 M24 710.0 1050.0 1230.0 Three things worth knowing about torque on socket head cap screws: Lubrication changes everything. A lubricated thread reduces friction by around 20% — which means the same torque produces 20% more clamping force. Apply the dry torque to a lubricated thread and you may yield the bolt. Apply the lubricated torque to a dry thread and you may not develop full preload. Re-used cap screws should not be re-torqued to the same value. A Class 12.9 screw that has been torqued to specification once is partially work-hardened and may have begun to yield. For critical joints, replace the screw rather than re-use it. The torque wrench must be calibrated. A miscalibrated wrench is worse than no torque wrench at all — it gives you false confidence in a wrong number. See our Torque Wrench Calibration Guide for calibration intervals and methods. How to Install Socket Head Cap Screws Correctly Socket head cap screws look simple to install — drop them in and tighten. But the failure modes are predictable, and almost all of them come from the same handful of installation errors. Step 1 — Verify the screw matches the joint design Confirm thread size, length, grade, and material against the assembly drawing or original part. If you are replacing a screw that has failed, replace it with the same grade or higher — never lower. Step 2 — Inspect the threads Run a finger over the threads. They should be clean and smooth — no burrs, no debris, no rust. A damaged screw should not be installed; a damaged thread in the parent material should be chased with a tap before fitting. Step 3 — Lubricate where appropriate Stainless threads: always apply anti-seize or a thread lubricant. Galling is otherwise inevitable. Carbon steel threads in dry indoor environments: light oil or running thread sealant if vibration is a concern. A small amount of thread-locking compound may be specified — see our Thread Locking & Sealing Guide. Hot, food-grade or pharmaceutical environments: use a food-grade or high-temperature anti-seize as specified. Step 4 — Add the correct washer Always use a washer under the head where vibration is a possibility, where the bearing surface is soft (aluminium, plastic), or where the screw must clamp through a slotted hole. Use a flat washer to spread load and protect the surface; use a spring washer or nylon-insert nut to resist vibration loosening. For a complete washer reference, see our Types of Washers Guide. Step 5 — Engage the Allen key fully Push the hex key fully down into the socket before applying torque. A partly-engaged key contacts only the upper portion of the socket and concentrates stress on the shallow walls. This is the single most common cause of stripped sockets — fitting the key under load instead of seating it first. Step 6 — Tighten in the correct sequence For multi-bolt joints (gearbox covers, machine bases, flange connections), tighten in a star or cross-pattern sequence to draw the joint down evenly. Never tighten one bolt fully before starting the next on a flange — uneven loading cocks the joint and can crack the casting. Three passes is standard: first pass to roughly 30% of final torque, second to 75%, third to full torque. Step 7 — Use a calibrated torque wrench for critical joints For high-strength engineered joints (Class 12.9 dies, gearbox bolts, structural fixings), torque every screw with a calibrated wrench. For non-critical applications, "tight" by feel may be acceptable — but document which joints are which in your maintenance procedure. Installation checklist: Right grade ✓ — clean threads ✓ — lubricant applied (stainless or as specified) ✓ — washer fitted (where required) ✓ — hex key fully seated ✓ — star-pattern tightening on multi-bolt joints ✓ — calibrated torque wrench on critical joints ✓. How to Remove a Stripped Socket Head Cap Screw A stripped socket head cap screw — where the hex socket has rounded out and the Allen key spins freely inside — is one of the more common workshop frustrations. There are five removal methods, ordered from least invasive to last resort. Try them in this sequence; do not jump ahead. (For a broken or seized stud rather than a stripped cap screw — different geometry, different tool — see our Stud Extractor Guide.) Method 1 — Increase grip in the existing socket The first attempt should always be to grip the rounded socket better. Two field tricks work surprisingly often: Rubber band trick: push a wide rubber band into the socket, press the hex key firmly down through it, and turn slowly. The rubber fills the gap between the rounded socket walls and the hex key, increasing friction. Steel wool or aluminium foil: same principle — pack a small piece of steel wool or crumpled foil into the socket and engage the key through it. This works in roughly 30% of cases — particularly where the socket is only lightly rounded. Method 2 — Use a Torx bit one size larger If the rubber band fails, the next move is a Torx (star) bit hammered into the socket. The Torx bit's points dig into the rounded hex walls and provide grip. Choose a bit one size larger than the original hex socket — for example, a T30 Torx for an M8 (6 mm hex) cap screw. Hammer the bit firmly into the socket with a soft-faced hammer until it seats, then turn with a wrench or impact driver. This works in another 30–40% of cases. Method 3 — Apply penetrating oil and wait If the screw is corroded into its thread (common on outdoor or wet-environment installations), the rounded socket may not be the only problem. Apply a quality penetrating oil — see our Penetrating Oil Guide — and wait 24 hours. Tap the head lightly with a hammer to vibrate the oil into the threads. Re-attempt Method 1 or 2 after the wait. Method 4 — Drill out and use a screw extractor Where the socket is fully destroyed and grip cannot be re-established, the next step is to drill a small pilot hole down the centre of the screw and drive a screw extractor (a left-hand tapered tool with reverse threads). The extractor bites into the drilled hole and turns the screw out as you turn the wrench anti-clockwise. Use a left-hand drill bit if you have one — sometimes the heat and reverse rotation alone will free the screw before the extractor is even needed. Method 5 — Drill out completely or weld a nut The last resorts: Drill out: with a series of progressively larger drill bits, drill the screw out completely until only the threaded shell remains in the parent material. The shell can then be picked out or re-tapped to a larger size. Weld a nut to the head: for cases where the head is still proud of the surface, weld a hex nut to the top of the cap screw head and turn the screw out using a spanner on the welded nut. The weld heat also helps break thread corrosion. This is a common shop technique on heavily seized cap screws. The most common cause of stripped sockets is using the wrong key size or a worn key. An imperial 3/16" key in an M5 cap screw (4 mm metric) feels close but rounds the socket within seconds. A bent or burred long-arm key contacts at the corners, not the flats. Replace worn keys, never mix metric and imperial drivers, and always seat the key fully before applying torque. Brands of Socket Head Cap Screw at AIMS Industrial The full AIMS range of socket head cap screws is available at browse the AIMS Industrial socket head cap screw collection here. The key brands stocked, by application: Bremick Australian-owned fastener supplier — broad range of metric DIN 912 socket head cap screws in Class 8.8 zinc-plated and Class 12.9 black oxide. Reliable stock availability for general industrial work, sized M3 through M30. The default choice for most workshop and maintenance applications where quality and price both matter. Hobson Engineering Specialist fastener supplier with engineering-grade stock. DIN 912 cap screws in carbon steel and stainless, including 304 and 316 in metric and imperial sizes. Strong choice for precision engineering and applications where certified material and traceability are required. Inox World Stainless-only specialist — A2 (304) and A4 (316) socket head cap screws across the full metric size range. Used where corrosion resistance is the primary requirement: marine, food processing, pharmaceutical, and outdoor coastal applications. Proper stainless property class marking on every part. SOKO European-manufactured high-quality socket head cap screws, particularly strong in Class 12.9 black oxide for precision engineering. Used where consistent metallurgy and dimensional accuracy matter — die work, jig and fixture building, gearbox manufacture. Bumax Swedish high-strength stainless specialist. Bumax 88 and Bumax 109 grades provide tensile strength approaching Class 8.8 and 10.9 carbon steel respectively, in a fully stainless body. Used in offshore, defence, motorsport, and any application where standard 316 lacks the strength and carbon steel cannot survive the environment. Specified by name on engineering drawings. For full stock availability, sizes, and pricing across all five brands: browse the AIMS Industrial socket head cap screw collection. For pairing with the right nut, see our Types of Nuts Guide; for the right washer, see our Types of Washers Guide. Frequently Asked Questions What is a socket head cap screw? A socket head cap screw is a high-strength precision fastener with a cylindrical head and an internal hex (Allen) socket drive. It is also called an Allen bolt, cap screw, or socket bolt. Manufactured to DIN 912 (or the equivalent ISO 4762), it is used wherever a low-profile head, high-strength clamping, or recessed installation is required — machine bases, gearbox covers, dies, jigs, and engineered joints. What is a socket head cap screw also known as? In Australian workshops, the most common names are "Allen bolt", "cap screw", "Allen head screw", and "socket bolt". On engineering drawings and parts lists, you will see "socket head cap screw", "SHCS", "DIN 912", or "ISO 4762". All terms refer to the same fastener — a cylindrical-head screw driven by a hex (Allen) key. What is the difference between a socket head cap screw and a hex bolt? A socket head cap screw has a cylindrical head with an internal hex socket — driven by an Allen key from above. A hex bolt has a six-sided external head — driven by a spanner or socket from the side. Socket head cap screws fit into recessed or counterbored holes where a spanner cannot reach, and are typically supplied at higher property classes (Class 12.9 standard). Hex bolts are most commonly Class 8.8 or 10.9 and require side clearance for the spanner. What does DIN 912 mean on a fastener? DIN 912 is the German national standard that defines the dimensions, tolerances, and material properties of socket head cap screws — head diameter, head height, hex socket size across flats, thread tolerance, and grade designations from M1.6 through M64. It is the most widely cited socket head cap screw standard in industrial supply. ISO 4762 is the equivalent international standard and is dimensionally compatible with DIN 912. How do I measure a socket head cap screw? Five measurements identify a socket head cap screw: thread diameter (e.g. M8), thread pitch (typically coarse, 1.25 mm for M8), length (measured from under the head to the end of the thread, NOT including the head), head diameter (across the cylindrical body), and hex socket size (across flats). The standard parts-list format is "M[size] × [length] SHCS, Class [grade], [material]" — for example, "M10 × 40 SHCS, Class 12.9, black oxide". What is the difference between Grade 8.8, 10.9 and 12.9 socket head cap screws? The two-part grade number indicates strength. The first digit relates to ultimate tensile strength in 100-MPa units; the second relates to the yield-to-tensile ratio. Class 8.8 has 800 MPa tensile, 640 MPa yield. Class 10.9 has 1040 MPa tensile, 940 MPa yield. Class 12.9 has 1220 MPa tensile, 1100 MPa yield. Class 12.9 is the standard grade for socket head cap screws and is the engineering default — never substitute a lower grade without re-engineering the joint. Can I use a stainless socket head cap screw instead of a steel Class 12.9? Not as a direct substitute. Standard 304 (A2-70) and 316 (A4-70) stainless socket head cap screws have tensile strength around 700 MPa — closer to Class 8.8 carbon steel than Class 12.9. Replacing a Class 12.9 with stainless reduces clamping capacity by approximately 40%, which can cause vibration loosening, joint fatigue, or failure. For high-strength stainless applications, specify Bumax 88 (≈ Class 8.8 strength) or Bumax 109 (≈ Class 10.9 strength) — both available at AIMS Industrial. What size Allen key do I need for an M8 socket head cap screw? An M8 socket head cap screw to DIN 912 takes a 6 mm Allen key (hex key) across flats. Other common metric sizes: M3 = 2.5 mm, M4 = 3 mm, M5 = 4 mm, M6 = 5 mm, M8 = 6 mm, M10 = 8 mm, M12 = 10 mm, M16 = 14 mm, M20 = 17 mm. Always use the correctly sized key — undersized or worn keys round out the socket. Imperial socket head cap screws use a different table and require imperial hex keys. What is the torque spec for an M10 socket head cap screw? For an M10 Class 12.9 socket head cap screw, indicative dry torque is approximately 84 Nm. For Class 10.9, around 72 Nm. For Class 8.8, around 49 Nm. These are dry-thread values — if the threads are lubricated or have anti-seize applied, reduce torque by approximately 15–25% to avoid over-stressing the fastener. Always defer to the equipment manufacturer's specified torque if one is given. What is the difference between a cap head and a button head socket screw? A cap head (DIN 912) has a tall cylindrical head and deep hex socket — designed for maximum strength and high-torque applications, the standard SHCS form. A button head (DIN 7380 / ISO 7380) has a low-profile rounded head and shallower socket — used where head clearance is limited or where a softer cosmetic finish is preferred. Button heads have approximately 30–40% lower torque rating than cap heads. Specify cap head for engineered joints; specify button head only where clearance or appearance matters more than maximum torque. How do I remove a stripped socket head cap screw? Try methods in order, starting least invasive: (1) pack a rubber band, foil or steel wool into the rounded socket and re-engage the Allen key for additional grip; (2) hammer a Torx (star) bit one size larger than the hex socket into the head — the points bite into the rounded walls; (3) apply penetrating oil and wait 24 hours if corrosion is suspected; (4) drill a pilot hole and drive a screw extractor with a tap wrench; (5) for the most severe cases, drill out the screw entirely or weld a hex nut to the head and turn out with a spanner. The most common prevention: use the correct hex key size, replace worn keys, and never mix metric and imperial drivers. What is the difference between Grade 304 and Grade 316 stainless socket head cap screws? Grade 304 (A2) stainless contains chromium and nickel — suitable for general indoor use, food processing without chlorides, and most outdoor applications away from salt water. Grade 316 (A4) adds molybdenum, providing resistance to chloride attack — required for marine work, coastal industrial sites, chlorinated swimming pools, food processing brines, and chemical environments. Grade 316 is approximately 30% more expensive than 304. For any AU coastal application within 1 km of the surf, specify 316. Need the right spanner for that bolt? Our Spanner Size Chart lists every common metric and imperial size. People Also Ask — Socket Head Cap Screws Q: What is a socket head cap screw and what makes it different from a standard hex bolt? A: A socket head cap screw (also called an Allen bolt or hex socket cap screw) has a cylindrical head with a hexagonal internal recess (socket) that is driven with an Allen key (hex key). The compact cylindrical head allows it to be used in recessed or countersunk positions where a standard hex bolt head would not fit. Socket head cap screws are typically manufactured to higher strength grades than equivalent standard hex bolts and are commonly used in machinery, tooling, and precision engineering applications. Q: What grade and material options are available for socket head cap screws? A: Socket head cap screws are most commonly supplied in property class 12.9 (alloy steel, black oxide finish) and 8.8 (medium carbon steel). Stainless steel versions (typically A2-70 in grade 304, or A4-80 in grade 316) are available for corrosion-resistant applications. Titanium socket head cap screws are used in weight-critical aerospace and high-performance applications. For food, pharmaceutical, or chemical environments, grade 316 stainless is the standard choice. Always verify the grade marking on the head or packaging. Q: How do I determine the correct torque for tightening a socket head cap screw? A: Torque values for socket head cap screws are calculated based on the fastener's property class, thread pitch, thread diameter, friction coefficient, and the materials being joined. Consult the manufacturer's torque table for the specific property class and size. Higher-strength grades (such as 12.9) command higher torques than lower-strength grades of the same size. Lubricated threads reduce friction and require a lower applied torque to achieve the same clamp load — apply the lubricated-thread correction factor specified in the torque table. Q: Can I use a standard hex key or do I need a calibrated torque wrench for socket head screws? A: A standard hex key is suitable for general assembly at typical torques. For critical structural or mechanical joints where specific preload is essential — such as fixture clamping, precision toolholding, or pressure-bearing assemblies — a torque wrench with the correct hex bit should be used to achieve the required clamp load accurately. Overtorquing a socket head cap screw with a standard L-key is common, as the short arm provides enough leverage to yield the fastener. An L-key with a short ball end on the driving arm provides a tactile warning when approaching the yield point. Q: What causes the hex socket in a socket head cap screw to round out? A: The internal hex socket rounds out when excessive torque is applied, when the wrong-sized key is used (even a slightly undersized key causes rocking and point loading), or when the key is worn and no longer seats squarely. Using the correct nominal key size is the primary prevention — metric and imperial keys are not interchangeable. A quality hex key or hex-bit socket in hardened steel with a correct machined fit distributes force evenly across all six faces. If a socket is already partially rounded, a screw extractor kit or an oversized tapered hex key can often still remove it. For pan head screws, see our pan head screws range stocked across Australia.
Read moreLoctite 222: Purple Low-Strength Threadlocker Guide
Purple low-strength threadlocker for fasteners under 6mm. Cure times, breakaway torque, 222 vs 243, Activator 7471 for inactive metals, and the 222MS Mil-Spec variant — explained.
Read moreCompression Springs Explained: Types, Dimensions, Spring Rate and How to Select the Right One
Compression springs are everywhere — inside valves, machine tool fixtures, door latches, industrial equipment, and workshop jigs. Most of the time you don't notice them until one fails and you need a replacement. That is when the selection process matters, and it is more specific than many people expect. The wrong free length, wire diameter, or spring rate will either make the spring useless or over-stress it into early failure. This guide covers the four main types, the four end configurations, the six key dimensions you need to measure, how spring rate works, which material to choose, and when an assortment kit is smarter than specifying an individual spring. If you need to identify or replace a compression spring, start here. For an overview of all spring types — extension, torsion, gas struts, leaf, Belleville disc and constant force springs — see our Types of Springs Guide. This guide focuses specifically on compression springs. How Compression Springs Work A compression spring is a helical coil of metal wire designed to resist compressive axial force. When a load is applied along the spring axis, the coils deflect — moving closer together — and the spring stores that energy elastically. Remove the load and the spring returns to its original length, releasing the stored energy as a push force. The key characteristic is that the coils are open (spaced apart) in their free, unloaded state. This distinguishes compression springs from extension springs, where coils are tightly wound together, and torsion springs, which resist rotational force rather than axial compression. The relationship between force and deflection is linear for most compression springs operating within their working range — apply twice the force, get twice the deflection. This linearity is expressed as the spring rate (also called spring constant or stiffness), measured in Newtons per millimetre (N/mm) or pounds per inch (lb/in). Types of Compression Springs Most stock compression springs are cylindrical helical springs — constant diameter from end to end. Three other profiles exist for specific applications where standard cylindrical springs have limitations. Cylindrical (helical) compression springs The standard type. Consistent coil diameter from end to end, predictable linear spring rate, easy to manufacture and stock. This is what most industrial suppliers, including AIMS, carry as standard assortment sizes. Suitable for the vast majority of maintenance and repair applications. Conical compression springs Cone-shaped: one end has a larger coil diameter that tapers to a smaller diameter at the other end. When fully compressed, each coil nests inside the next, achieving a solid height as low as a single wire diameter — far lower than a cylindrical spring of equivalent travel. Used where installed height is severely restricted, such as in valve seats, battery contacts, and circuit breakers. Conical springs also have inherently higher lateral stability and resist sideways buckling better than cylindrical springs of the same rate. Barrel (convex) compression springs Coil diameter is smallest at both ends and largest in the middle, like a barrel. The geometry reduces the tendency to buckle under load and provides a progressive spring rate — the rate increases as the spring is compressed because the outer coils close off first. Used in vehicle seats, mattresses, and applications needing anti-buckling without a guide rod. Also called convex or cushion springs. Hourglass (concave) compression springs The inverse of the barrel — largest diameter at both ends, smallest in the middle. Like conical springs, hourglass springs have improved lateral stability and resist buckling. The nested coil geometry also allows a very low solid height. Less common in standard stock; usually specified or custom-made for particular applications. Compression Spring End Types How the ends of a compression spring are formed has a direct effect on how it seats, how square it sits under load, and whether it needs a guide rod or housing. There are four configurations. Open ends (plain) The coil pitch continues right to the end of the wire — no change in spacing, no closing of the final coil. The end of the wire is simply cut. Open-end springs are the cheapest to manufacture but do not sit flat. They are designed to operate over a rod or inside a housing that controls alignment. Not suitable for free-standing applications where squareness under load matters. Closed ends (squared) The final coil at each end is wound tight against the adjacent coil, closing off the pitch. This creates a flatter bearing surface and makes the spring more self-supporting. Closed ends are the most common configuration in stock springs and general-purpose applications. Also called squared ends. Closed and ground ends After the end coils are closed, the ends are precision-ground flat and perpendicular to the spring axis. This is the most precise configuration — it maximises squareness under load, minimises buckling tendency, and ensures consistent contact with the seat. Specified where accurate load positioning and long fatigue life are required, such as in precision machinery and valve springs. Adds cost over plain-closed ends but is often worth it in production or high-cycle applications. Open and ground ends Open-pitch ends that have been ground flat. Less common than the three configurations above. Used in specific applications requiring a low solid height with a flat bearing surface. Practical rule: For most workshop maintenance and general industrial repair work, closed ends (squared) are correct. If you are replacing a precision spring in machinery — especially anything with a defined seat — check whether the original is ground. Using an unground spring in a ground-spring application can introduce lateral error and accelerate wear. Key Dimensions Explained Six measurements define a compression spring. You need all six to specify a replacement correctly. Dimension What it is Why it matters Free length (FL) Length of the spring with no load applied Must fit the available installed height in its uncompressed state Outside diameter (OD) Outer diameter of the coil Must fit inside a housing or bore without binding Inside diameter (ID) Inner diameter of the coil Must clear a rod or shaft that the spring seats over Wire diameter (d) Diameter of the wire used to wind the spring Directly determines stiffness — small changes have a large effect on spring rate (rate varies with d⁴) Active coils (Na) Number of coils that actually deflect under load (total coils minus dead end coils) More active coils = lower spring rate; fewer = stiffer Solid height (Ls) Length when all coils are touching (fully compressed) The spring must never be compressed to solid height in service — this causes permanent set or failure Note on OD vs ID: Standard spring catalogues list OD. When measuring a spring to go over a rod, work from ID outward. Add at least 0.5–1.0 mm clearance between the rod and the spring ID to prevent binding as the spring deflects and its coils expand slightly in diameter. Working travel: The usable deflection range is the difference between free length and solid height, minus a minimum clearance of around 15–20% of that travel. Operating a spring repeatedly to its solid height causes coil clash, work-hardening, and permanent set. Size for the application load well within the working travel range. Spring Rate: What It Is and How to Calculate It Spring rate (k) is the force required to compress or extend a spring by one unit of length. In metric terms: k = F / x Where k = spring rate (N/mm), F = applied force (N), x = deflection from free length (mm) For a helical compression spring, the spring rate is determined by four geometric and material factors: k = (G × d⁴) / (8 × D³ × Na) Where G = shear modulus of the material (N/mm²), d = wire diameter (mm), D = mean coil diameter (mm), Na = number of active coils You do not need to calculate this from first principles for a replacement spring — but the formula tells you what the variables are and how sensitive rate is to each: Wire diameter has a fourth-power effect — increase wire diameter by 10% and spring rate rises by about 46%. A very small change in wire size produces a large stiffness change. Mean coil diameter has a cubic inverse effect — wider coils produce a softer spring. Adding coils softens the rate proportionally; removing coils stiffens it. When selecting a replacement, match the spring rate as closely as the available stock allows. A spring with a significantly higher rate than the original will apply too much force at the working deflection; one with a lower rate may not generate enough closing or return force for the mechanism to function correctly. Materials Most stock compression springs are made from one of three materials. The right choice depends on the operating environment. Material Also called Best for Avoid when High-carbon steel (music wire) Music wire, hard-drawn wire, carbon steel spring wire Indoor, dry environments. Highest tensile strength of any spring wire. Excellent fatigue life. Best value for standard workshop and machinery applications. Exposed to moisture, chemicals, or corrosive environments — will rust without surface treatment. Stainless steel 316 (A4) SS316, marine grade stainless Wet, marine, food processing, or chemically exposed environments. Good corrosion resistance. Slightly lower tensile strength than music wire for the same diameter. High-temperature applications above ~300°C (316 loses temper). Also costs more than carbon steel. Stainless steel 302/304 (A2) SS302, SS304 General corrosion resistance where 316 is not required. Common in food and light industrial environments. Marine or chloride-heavy environments — 302/304 is less resistant to chloride pitting than 316. Phosphor bronze PB, CuSn alloy Electrical conductivity requirements, seawater immersion, non-magnetic applications. Good corrosion resistance in marine environments. High-load applications — lower tensile strength than steel. Higher cost than stainless. For the majority of Australian industrial and workshop applications — plant maintenance, jigs and fixtures, tooling, general machinery — high-carbon steel springs are the standard choice. Upgrade to 316 stainless for any outdoor, wash-down, coastal, or food-production environment. How to Select the Right Compression Spring Follow these steps in order to identify or specify a replacement spring. Step 1 — Measure free length With no load on the spring, measure end to end. This is your starting point. If you are measuring a failed spring, check whether it has taken a permanent set — a spring that has shortened under overload will give a false free length reading. Step 2 — Measure OD and ID Use calipers for accuracy. Note both OD and ID, then confirm which dimension is constrained by the application (inside a bore = OD critical; over a rod = ID critical). Allow 0.5–1.0 mm clearance for deflection. Step 3 — Measure wire diameter Calipers across a single coil wire. This is the most critical measurement for getting spring rate close to the original. Even a 0.1 mm difference in wire diameter can shift the rate meaningfully on small springs. Step 4 — Count active coils Count total coils, then subtract 1.5–2 coils for ground and closed end types (these are the inactive/dead coils at each end). Active coil count, combined with wire diameter and coil diameter, determines spring rate. Step 5 — Confirm solid height Compress the spring fully by hand or in a vice until all coils touch. The length at this point must be less than the compressed working height in the application. If solid height is too long for the housing, the spring will bottom out in service. Step 6 — Match material to environment Default to carbon steel for dry, indoor use. Specify stainless 316 for any wet, coastal, or chemically exposed location. Step 7 — Check load or rate requirement If you know the force the spring must exert at its working length, calculate the required rate: k = F / (free length − working length). Compare this to the rate of the stock spring you are considering. A ±20% tolerance on spring rate is generally acceptable for non-precision replacement work. Assortment Kits vs. Individual Springs For workshop maintenance and general repair work, an assortment kit is almost always more practical than specifying individual springs. The reason is straightforward: you rarely know exactly which spring has failed until you are standing in front of the equipment, and ordering individual springs involves lead time that a stocked kit avoids. AIMS stocks Champion compression spring assortment kits in both carbon steel and stainless steel 316, covering a range of diameters and lengths suited to common industrial and workshop applications. These are the two options: Champion CA102 — 72-piece carbon steel compression spring assortment. Covers the most common OD, wire diameter, and length combinations for standard machinery and tooling maintenance. Champion CA1802 — 72-piece stainless steel 316 (A4) compression spring assortment. The stainless equivalent for wet, coastal, or food-grade environments. GJ Works GKA92 — 90-piece imperial compression and extension spring set, suitable for older machinery and equipment with imperial spring specifications. Individual Champion carbon steel and stainless 316 springs are also available for applications where a specific size is needed in quantity. A kit on the shelf beats a lead time every time. For any workshop that regularly services machinery, it is a practical investment. Custom Compression Springs Standard stock springs cover the majority of industrial replacement needs. However, there are applications — specific force requirements, unusual dimensions, non-standard materials, or production quantities — where a standard spring cannot be made to work. In these cases, custom-manufactured springs are the right answer. AIMS may be able to assist with sourcing custom compression springs depending on your specification. Contact the AIMS team with your full spring spec — free length, OD, wire diameter, active coils, material, end type, and required rate or load at deflection — and we can advise on options and lead times. Common Industrial Applications Compression springs appear across a wide range of industrial and workshop applications: Machine tooling and jigs — return springs in clamps, die springs in punch and press tooling, ejector springs in injection moulds Valves and flow control — valve seat springs in pneumatic and hydraulic systems, check valve springs, pressure relief valve springs Assembly and fastening — spring-loaded plungers, detent mechanisms, push-button assemblies Conveyor and materials handling — tension-take-up systems, over-centre mechanisms, spring-loaded guides Electrical and electronics — battery contacts, circuit breaker components, relay springs Automotive and mobile equipment — suspension bump stops, throttle return springs, door and hatch mechanisms General maintenance — replacing worn or failed springs in any plant or facility maintenance context Frequently Asked Questions What is a compression spring? A compression spring is a helical coil spring designed to resist compressive axial force. Its coils are open (spaced apart) in the free state. When compressed, the coils move together and the spring stores energy elastically. When the load is removed, the spring pushes back to its original free length. Compression springs are the most common spring type in industrial and mechanical applications. How does a compression spring work? When a compressive force is applied along the axis of the spring, the coils deflect toward each other in proportion to the force applied. This relationship is linear — described by the spring rate (k = F/x) — meaning twice the force produces twice the deflection within the working range. The spring stores the energy elastically in the wire material and releases it as a push force when the load is removed. What are the different types of compression springs? The four main types are: cylindrical (constant diameter, most common), conical (tapers from large to small diameter, very low solid height), barrel or convex (widest in the middle, anti-buckling), and hourglass or concave (widest at both ends, used for specific stability requirements). Standard stock springs are cylindrical. The other three are selected for applications where the cylindrical form has a specific limitation. What is spring rate and how is it calculated? Spring rate (k) is the force required to deflect a spring by one unit of length, expressed as N/mm (metric) or lb/in (imperial). It is calculated as k = F / x (force divided by deflection). For a helical compression spring, rate is determined by material shear modulus, wire diameter (to the fourth power), mean coil diameter (cubed, inverse), and number of active coils. Wire diameter has the largest effect: a 10% increase in wire diameter raises spring rate by approximately 46%. What are the different end types for compression springs? Four configurations exist: open (plain) ends where the pitch continues to the wire tip — these require a rod or housing for support; closed (squared) ends where the final coil winds tight against the adjacent coil for a flatter bearing surface; closed and ground ends where the squared ends are precision-ground flat and perpendicular — the most precise configuration for load-critical applications; and open and ground ends. For general industrial and workshop replacement work, closed (squared) ends are the standard choice. What is solid height and why does it matter? Solid height is the length of the spring when fully compressed — all coils touching. It equals wire diameter multiplied by total coil count. In service, the spring must never be compressed to solid height. Repeatedly bottoming out a spring causes coil clash, work-hardening, and permanent set (the spring stays shorter and loses rate). Always confirm the solid height is smaller than the minimum compressed length in the application by at least 15–20% of the available travel. What materials are compression springs made from? Most stock springs are high-carbon steel (music wire) for indoor and dry applications — highest tensile strength and best value. Stainless steel 316 (A4) is specified for wet, coastal, marine, or food processing environments due to its corrosion resistance. Stainless 302/304 (A2) is used for lighter corrosion resistance requirements. Phosphor bronze is used where electrical conductivity, non-magnetic properties, or seawater immersion is required. Chrome silicon and Inconel alloys are used for high-temperature and high-cycle fatigue applications, typically in custom-specified springs. How do I measure a compression spring for replacement? Measure six dimensions: (1) free length — overall length with no load; (2) outside diameter (OD); (3) inside diameter (ID); (4) wire diameter — use calipers across a single coil wire; (5) total coil count; (6) solid height — compress fully until coils touch. From these you can calculate spring rate and match to a stock spring. Note whether the ends are open or closed, and whether they are ground. If the spring has failed through permanent set (shortened), estimate the original free length from the application's housing depth. What is the difference between a compression spring and an extension spring? Compression springs have open, spaced coils and resist compressive (push) forces. Extension springs have tightly wound coils with formed hooks or loops at each end, and resist tensile (pull) forces — they stretch under load rather than compress. The operating direction is opposite: compression springs push back when squeezed; extension springs pull back when stretched. Extension springs also have an initial tension that must be overcome before the coils begin to open. What is the difference between a compression spring and a torsion spring? Compression springs resist axial (push/pull) force along the spring axis. Torsion springs resist rotational (twisting) force — they are designed to wind tighter or unwind when torque is applied to their legs. Torsion springs are found in door hinges, clothespins, window latches, and garage door mechanisms. The wire in a torsion spring is loaded in bending rather than torsion (despite the name), which affects material selection and fatigue behaviour differently from compression spring design. What happens if a compression spring is compressed too much? Over-compression causes coil clash — the coils impact each other at solid height — which induces shock loading, surface damage, and work-hardening in the wire material. Repeated over-compression leads to permanent set: the spring takes a shorter free length and reduced rate, meaning it can no longer exert the correct force at the working deflection. In extreme overload, the spring yields plastically or fractures. Always design and select so the working deflection leaves at least 15–20% of available travel as a buffer above solid height. Can compression springs be custom made? Yes. When standard stock springs cannot meet the required free length, OD, wire diameter, spring rate, or material specification, custom-manufactured springs are available. AIMS may be able to assist with sourcing custom compression springs for specific applications. Contact the AIMS team with your full specification — free length, outside diameter, wire diameter, number of coils, material, end type, and required rate or load — and we can advise on options and lead times. Shop Compression Springs at AIMS Industrial AIMS stocks compression springs in carbon steel and stainless steel 316, available as individual springs and as assortment kits for workshop and maintenance applications. Browse the full compression springs range at AIMS Industrial — including Champion assortment kits in carbon steel and stainless 316, individual compression springs by size, and imperial spring sets for older equipment. Need a spring that isn't in our standard range? Contact the AIMS team with your specification and we will advise on custom options and lead times. People Also Ask — Compression Springs Q: What is a compression spring and how does it work? A compression spring is an open-coil helical spring designed to resist compressive forces. When a load is applied along its axis the coils compress together, storing energy proportional to the deflection. When the load is removed the spring returns to its free length, making it suitable for applications requiring a restoring force such as valves, latches, switches and cushioning mechanisms. Q: How is a compression spring's rate calculated? Spring rate is the force required to compress the spring by one unit of length, expressed in N/mm or lbf/in. It is determined by the wire diameter, mean coil diameter, number of active coils and the shear modulus of the wire material. A higher spring rate means a stiffer spring; a lower rate produces a softer, more compliant spring. Q: What is the difference between open and closed (ground) ends on a compression spring? Open-ended springs have coils that continue at the same pitch to each end, giving an uneven bearing surface. Closed (squared) ends have the last coil brought perpendicular to the spring axis; closed and ground ends are also machined flat, providing a stable bearing surface and more accurate load application. Ground ends are preferred where precise loading and squareness are important. Q: What causes a compression spring to fatigue or break prematurely? Common causes include operating above the spring's maximum deflection, inadequate surface finish or nicks that initiate cracks, corrosion particularly in marine or chemical environments, and operating beyond the material's fatigue limit through high-cycle repeated loading. Selecting the correct wire material and surface treatment for the application conditions is the primary preventive measure. Looking for o-rings and o-ring kits? Our o-rings and o-ring kits range covers the common sizes and brands.
Read moreCountersunk Screw Guide: Types, Angles & How to Countersink Correctly
The table below covers standard metric socket countersunk screws to ISO 10642 (DIN 7991). Head dimensions are maximum nominal values.
Read moreCoach Bolt & Coach Screw Guide: Sizes & Pilot Holes
What Is a Coach Bolt? A coach bolt (also called a cup head bolt or carriage bolt) is a fastener with a smooth domed head, a square shoulder under the head that locks into timber to prevent the bolt rotating during tightening, and a metric or imperial threaded shank. It's used with a nut and washer to clamp two pieces of timber, or timber to metal, where you want a clean rounded finish on one side. What's the difference between a coach bolt and a coach screw? A coach bolt goes all the way through both parts and is tightened with a nut on the back. A coach screw threads directly into timber like a heavy-duty wood screw, with a hex head you drive with a spanner — no nut required. Use coach bolts when you can access both sides; coach screws when you can't. Are coach bolts the same as carriage bolts? Yes. "Coach bolt" is the Australian and UK term; "carriage bolt" is the US term for the same fastener. If you have searched for coach bolts and ended up more confused than when you started — wondering whether you need a coach bolt or a coach screw, what clearance hole to drill, or why the supplier's catalogue calls them cup head bolts — this guide covers it all. Coach bolts and coach screws are two different products that share a name and often share a shelf. Both are used in timber construction — decking, fencing, pergolas, structural framing, agricultural and playground equipment — but they work in fundamentally different ways and are not interchangeable. Understanding which one you need, in what size and finish, is the practical focus of this guide. All specifications and standards referenced here are metric and Australian. Bookmark our Engineering Reference Charts hub for related sizing tables, conversion charts and Australian standard references across 9 topic clusters. Coach Bolt Sizes: Metric Dimensions — Quick Reference Coach bolts are specified by diameter × length. The length is measured from the underside of the head to the end of the thread. Size Shank Ø (mm) Clearance Hole (mm) Head Ø (approx) Common Lengths (mm) Nut Size (spanner) M6 6 6.5 14mm 20, 25, 30, 40, 50, 60, 75, 100 10mm M8 8 8.5 18mm 20, 25, 30, 40, 50, 60, 75, 100, 120, 150 13mm M10 10 10.5 22mm 25, 30, 40, 50, 60, 75, 100, 130, 150, 200 17mm M12 12 13 27mm 30, 40, 50, 60, 75, 100, 130, 150, 200, 250 19mm M16 16 17 34mm 40, 50, 60, 75, 100, 130, 150, 200, 250, 300 24mm M20 20 21 40mm 50, 60, 75, 100, 130, 150, 200, 250, 300 30mm What Is a Coach Bolt? A coach bolt (also called a cup head bolt in Australian supply catalogues, or a carriage bolt in US and sometimes New Zealand usage) is a through-bolt with a distinctive domed head and a short square neck immediately below it. Coach bolts follow standard metric diameter and thread sizing — for the full metric bolt reference across all head profiles see the AIMS Metric Bolt Size Guide. The dome is smooth — there is no slot, hex socket, or recess for a driver. You cannot tighten a coach bolt from the head side. Instead, the square neck bites into the timber surface as the nut on the reverse side is tightened, locking the bolt against rotation and allowing the joint to be fully tightened with a spanner or socket from one side only. The bolt passes completely through all members being joined and is secured with a nut and flat washer on the reverse face. The washer spreads the clamping load to prevent the nut from pulling into the timber grain. Coach Bolt — Key Characteristics Domed, smooth head (no drive recess) Square neck below head prevents rotation during tightening Passes through all members — requires access to both faces Secured with a nut and washer on the reverse Australian standard: AS 1390 (Cup Head Bolts — Metric Series) Typical grade: 4.6 mild steel (structural: 8.8 high tensile) Common finish: hot-dip galvanised for outdoor use The smooth dome head is both a feature and a limitation. It gives a clean, tamper-resistant appearance on the visible face — useful for playground equipment and public structures — but means the bolt can only be tightened from the nut side. If you do not have access to the reverse face, a coach screw is the right choice instead. What Is a Coach Screw? A coach screw (also called a lag bolt or lag screw in US usage) is a large-diameter, heavy-duty fastener with a hexagonal head and a pointed, coarse self-tapping thread. Unlike a coach bolt, it does not require a nut — it threads directly into the timber and relies on thread engagement for its holding strength. Coach screws are driven with a spanner or socket from one side only. They are faster to install than coach bolts in applications where through-access is not available or practical: fixing ledger boards to wall framing, attaching brackets to posts, connecting rails to timber uprights. Coach Screw — Key Characteristics Hexagonal head — driven with spanner or socket wrench Coarse, self-tapping thread with pointed tip Screws into timber from one side only — no nut required Requires a pilot hole to prevent timber splitting No Australian-specific standard; commonly supplied to DIN 571 dimensions Typical grade: mild steel (not graded in the same system as bolts) Common finish: hot-dip galvanised for outdoor and treated timber use The hex head means a coach screw looks superficially similar to a hex bolt, but the thread form is completely different. A hex bolt has a machine thread for use with a nut or tapped hole; a coach screw has a wood thread that cuts directly into timber. Do not use a coach screw in a tapped metal hole, and do not substitute a hex bolt for a coach screw in timber — the machine thread will not hold. Coach Bolt vs Coach Screw: Key Differences The confusion between these two products is the most common question in this product category. Here is the comparison in full: Feature Coach Bolt Coach Screw Head style Smooth dome — no drive Hexagonal — spanner/socket Thread type Machine thread (metric coarse) Wood thread (coarse self-tapping) Fixing method Through-bolt: nut + washer on reverse Screws into timber — no nut Side access Both sides required One side only Pre-drilling Clearance hole (bolt shank + 0.5–1mm) Pilot hole (70–80% of shank dia.) Shear strength Higher — bears against both faces Lower — thread engagement only Removability Fully removable — undo nut Removable but timber thread degrades with repeated removal Installation speed Slower — drill, insert, nut, washer Faster — drill pilot, drive in Appearance (face side) Clean dome — no drive marks Hex head visible Australian standard AS 1390 DIN 571 (no AS equivalent) Is a Coach Bolt the Same as a Carriage Bolt? Yes. Coach bolt and carriage bolt refer to the same fastener — the difference is regional terminology. In Australia and the UK, the product is called a coach bolt. In the United States (and in some New Zealand catalogues), the same product is called a carriage bolt. If you are working from an imported design, a US manufacturer's specification, or an international structural timber connection guide, "carriage bolt" means coach bolt. The dimensions are the same in metric (M8, M10, M12 etc.) and the approximate imperial equivalents most commonly encountered are: 3/8" ≈ M10, 1/2" ≈ M12, 5/16" ≈ M8. You may also see "cup head bolt" in Australian supply catalogues — this is the same product again, named after the cup-shaped dome head, and it is what AS 1390 calls it officially. Coach Bolt Sizes: Metric Dimensions Coach bolts are specified by diameter × length. The length is measured from the underside of the head to the end of the thread. The square neck depth and head diameter vary by size but follow the proportions of AS 1390. Size Shank Ø (mm) Clearance Hole (mm) Head Ø (approx) Common Lengths (mm) Nut Size (spanner) M6 6 6.5 14mm 20, 25, 30, 40, 50, 60, 75, 100 10mm M8 8 8.5 18mm 20, 25, 30, 40, 50, 60, 75, 100, 120, 150 13mm M10 10 10.5 22mm 25, 30, 40, 50, 60, 75, 100, 130, 150, 200 17mm M12 12 13 27mm 30, 40, 50, 60, 75, 100, 130, 150, 200, 250 19mm M16 16 17 34mm 40, 50, 60, 75, 100, 130, 150, 200, 250, 300 24mm M20 20 21 40mm 50, 60, 75, 100, 130, 150, 200, 250, 300 30mm How Long Should Your Coach Bolts Be? The coach bolt must pass completely through all members plus allow enough thread engagement for the nut — a minimum of one full nut height (typically 1× bolt diameter) beyond the last member is the practical rule. For a 45mm decking post connection using M12 bolts, for example, total member thickness + 15–20mm for nut and washer gives your minimum bolt length. Buying slightly longer than necessary is generally better than too short — you can always trim excess thread with an angle grinder, but a bolt that doesn't reach the nut face is useless. Standard stock lengths are typically in 10–25mm increments; non-standard lengths are often available to order for large structural projects. For general reference on metric fastener dimensions, see our Fastener Reference Chart. Coach Screw Sizes & Pilot Hole Chart Coach screws are specified by diameter × length, measured from under the head to the tip. The pilot hole is critical — too small and you risk splitting the timber or snapping the screw; too large and the thread engagement is insufficient for the required holding load. The general rule: pilot hole diameter ≈ 70% of the shank diameter for softwood (pine, treated pine), ≈ 80% for hardwood (ironbark, spotted gum, hardwood decking). Always drill a full-depth pilot hole — not just a starter hole. Size Shank Ø (mm) Pilot Hole — Softwood Pilot Hole — Hardwood Head Ø (across flats) Common Lengths (mm) M6 6 3.5mm 4.5mm 10mm 30, 40, 50, 60, 75, 100 M8 8 5mm 6mm 13mm 30, 40, 50, 65, 75, 100, 120, 150 M10 10 6mm 7mm 17mm 40, 50, 65, 75, 100, 130, 150, 200 M12 12 7mm 9mm 19mm 40, 50, 65, 75, 100, 130, 150, 200, 250 M16 16 10mm 11mm 24mm 50, 65, 75, 100, 130, 150, 200, 250, 300 ⚠️ Hardwood pilot holes: Under-drilling in hardwood is the most common cause of coach screw head shear-off on site. If your drill press or impact driver is straining hard before the screw reaches depth, stop and re-drill the pilot hole to the hardwood specification. Forcing it will either snap the screw or strip the timber thread — neither is recoverable without redrilling. For drill bit sizing across all fastener types, see our Bolt Grade Chart. Hot-Dip Galvanised (HDG) The standard finish for outdoor structural coach bolts in Australia. Hot-dip galvanising immerses the fastener in molten zinc at approximately 450°C, producing a metallurgically bonded coating typically 45–85 microns thick. This provides genuine long-term corrosion protection suitable for outdoor exposure, treated timber, and the Australian coastal environment. HDG coach bolts will develop a dull grey patina over time as the zinc oxidises — this is normal and is the zinc sacrificially protecting the steel underneath. HDG is the correct specification for any exposed structural connection. Electroplated Zinc Electroplated (bright zinc) coach bolts have a thin coating (5–15 microns) applied electrically. This provides only light corrosion protection — adequate for indoor applications, sheltered conditions, and short-term outdoor use during construction. Electroplated coach bolts must not be used in permanently exposed outdoor connections, and must never be used in treated timber (see below). Electroplated bolts are typically cheaper and have a brighter appearance than HDG. If you are unsure which you are purchasing, check the product specification — "galvanised" without qualification in Australian hardware retail often means electroplated rather than hot-dip. Stainless Steel: A2 and A4 For coastal, marine, food processing, or chemical environments where zinc-coated fasteners will not provide adequate corrosion resistance, stainless steel coach bolts are specified. A2 (Grade 304) is suitable for most outdoor and mild marine environments. A4 (Grade 316) contains molybdenum and is specified for direct marine exposure, saltwater contact, and aggressive chemical environments. Stainless coach bolts are significantly more expensive than galvanised and have lower tensile strength than high-tensile steel bolts — use them where corrosion resistance is the primary requirement, not where structural strength is marginal. For a full explanation of stainless fastener grades, see our Stainless Steel Fastener Grades Guide. Treated Pine: The Critical Rule CCA (copper chrome arsenate) and ACQ (alkaline copper quaternary) treated pine — the green-tinted structural and outdoor timber used for decking frames, fence posts, pergola posts, and landscaping — are chemically aggressive to electroplated zinc fasteners. The copper compounds in the treatment accelerate zinc corrosion significantly. Electroplated coach bolts and coach screws installed in treated pine will typically corrode through within 2–5 years in outdoor conditions, causing structural failure that may not be visible from the surface until the connection is already seriously compromised. ⚠️ Treated timber rule: Always use hot-dip galvanised or stainless steel fasteners in CCA or ACQ treated pine. This applies to both coach bolts and coach screws. Never use electroplated zinc in treated timber for any outdoor or structural application. When to Use Coach Bolts vs Coach Screws The decision comes down to three factors: access, load type, and permanence. Situation Use Coach Bolt Use Coach Screw Access to both sides of joint ✅ Preferred for maximum strength ✅ Also works, faster One side only accessible ❌ Not possible ✅ Only option High shear load (lateral force) ✅ Stronger in shear ⚠️ Adequate for light-moderate loads Engineer-specified connection ✅ Often specified for structural joints ⚠️ Check drawing — do not substitute Decking boards to joists ⚠️ Overkill in most cases ✅ Standard practice Post to bearer / beam connection ✅ Recommended for primary structure ✅ Acceptable if properly sized Appearance matters (face side) ✅ Clean dome is less obtrusive ⚠️ Hex head more visible Playground or public structure ✅ Dome head reduces snagging hazard ⚠️ Hex head can snag clothing Speed of installation is priority ❌ Slower — nut and washer required ✅ Drill and drive If an engineer or building certifier has specified the connection, always use exactly what is specified. Do not substitute coach screws for coach bolts on structural drawings without written engineering approval — the load calculations are based on the specified fastener type and quantity. How to Install Coach Bolts Coach bolt installation is straightforward but requires the square neck to seat correctly — if it does not, the bolt will spin when you tighten the nut and you will not be able to complete the joint. Mark and clamp the joint. Clamp both members together in their final position before drilling. Moving them after drilling will misalign the holes. Drill the clearance hole. Use a drill bit 0.5–1mm larger than the bolt shank (e.g. 10.5mm for M10). Drill through all members in a single pass if possible — this ensures the holes are aligned. Use a sharp bit and firm, steady pressure to avoid tearout at the exit face. Insert the coach bolt from the face side. Push the bolt through the hole with the dome head sitting on the surface. The square neck should be positioned in the hole at the entry face. Seat the square neck. Tap the dome head firmly with a hammer — 2–3 moderate blows — to drive the square neck into the timber at the entry face. The square neck must embed fully to prevent the bolt from rotating during tightening. If the wood is very hard, use a punch and hammer to square up the entry hole slightly, or use a spanner on the nut while holding the head still. Fit washer and nut. Slide a flat washer over the thread from the reverse side (washer distributes load across the timber grain and prevents the nut from pulling through). Thread the nut on by hand. Tighten with a spanner or socket. Tighten firmly to the specified torque. The dome head should not rotate — if it does, the square neck has not seated. Stop, re-seat by tapping the head, then continue tightening. For the correct nut to use with metric coach bolts, see our Types of Nuts Guide. For washer selection, see our Types of Washers Guide. ⚠️ Square neck not seating? This typically happens in very dense hardwood or when the clearance hole is slightly too large for the square neck dimensions. Solution: use a chisel or punch to create a shallow square impression at the entry point, or apply a backing plate washer under the head to bridge the gap and allow the nut to pull everything tight. How to Install Coach Screws Coach screw installation is faster than coach bolts but requires a correctly sized pilot hole. Skipping or under-sizing the pilot hole is the most common cause of both splitting the timber and shearing the coach screw head on installation. Mark the fixing position. Mark centre points for each screw. Pre-drilling precisely on-centre is important — coach screws cannot be steered once started. Drill the pilot hole to full depth. Use the pilot hole sizes from the table above, matched to your timber species. Drill to the full penetration depth of the screw — not just a starter hole. A pilot hole that ends halfway means the final threads are forced through undrilled timber. Apply a small amount of wax or soap to the thread (optional but recommended). Running the thread lightly across a block of wax or a bar of soap reduces drive torque significantly in hardwood and reduces the risk of snapping the screw. Do not use oil-based lubricants — they can affect timber treatments. Start the screw by hand. Thread the screw into the pilot hole a few turns by hand to ensure it is running straight and not cross-threading. Drive with a socket wrench or impact driver (low speed). Use a socket matched to the hex head (see size table). If using an impact driver, use the lowest torque setting — impact drivers can easily snap M6–M8 coach screws in hardwood. For M10 and above in hardwood, a torque wrench at a controlled setting is preferable. Drive to depth. The screw is correctly seated when the head bears firmly against the timber surface (or a washer, if specified). Do not overtighten — coach screws in timber can strip the thread engagement if over-driven. For help choosing the right screwdriver or socket for driving, see our Screwdriver Types Guide. Common Applications in Australian Construction Decking Coach screws (M8 or M10, HDG or stainless, 65–100mm long depending on deck board and joist thickness) are the standard fastener for attaching deck boards to joists and for fixing ledger boards to wall framing. For post-to-bearer connections and primary structural joints under the deck frame, M12 or M16 coach bolts through both members are the stronger choice where access allows. Always use HDG or stainless fasteners in treated pine decking frames. Specify the timber treatment type (CCA, ACQ, H3, H5) before purchasing fasteners — some timber treatment systems have specific fastener requirements beyond simple HDG. Fencing Coach screws (M8–M10, 65–100mm, HDG) are standard for attaching timber rails to posts. Coach bolts are used where maximum pull-out resistance is needed — gate hinge attachments, structural post-to-rail connections on farm and rural fencing, or anywhere the fence is subject to significant lateral load such as vehicle impacts or stock pressure. Pergolas and Outdoor Structures Both fastener types are used in pergola construction. Coach screws fix rafters to beams and beams to posts from the face side. Coach bolts are used for primary structural connections — post bases, beam splices, and any connection specified by the engineer or building certifier. Always use HDG in all outdoor timber-to-timber connections. Playground and Public Equipment Coach bolts with dome heads are preferred for exposed connections in playground equipment and public furniture because the smooth dome does not snag clothing and presents no projecting edges. Stainless steel (A2 or A4) is often specified for vandal resistance and the extended service intervals required in public infrastructure. Agricultural and Rural Applications Coach bolts (M12–M20, HDG) are widely used in stockyard construction, loading ramps, cattle crush assemblies, and farm shed framing. Sizes are larger and bolt lengths are longer than residential applications. Check whether the design uses metric or imperial specifications — older farm structures and some imported agricultural equipment use imperial carriage bolt sizes. Frequently Asked Questions What is a coach bolt used for? Coach bolts are used to join timber members where both sides of the joint are accessible, such as decking posts, fence rails, playground equipment, gate hardware, and structural timber framing. The domed head sits on the face side while a nut and washer are tightened from the reverse, creating a strong through-bolted connection resistant to shear and pull-through forces. What is the difference between a coach bolt and a coach screw? A coach bolt has a smooth domed head with a square neck and requires a nut and washer on the reverse — it goes completely through all members. A coach screw has a hexagonal head and a self-tapping thread that screws directly into timber from one side with no nut. Coach bolts are stronger in shear; coach screws are faster and require single-side access only. Is a coach bolt the same as a carriage bolt? Yes. Coach bolt (Australia, UK) and carriage bolt (US, sometimes NZ) are the same fastener. If you are working from a US specification, carriage bolt means coach bolt. The metric dimensions are the same; approximate imperial equivalents are 5/16" ≈ M8, 3/8" ≈ M10, 1/2" ≈ M12. Is a coach bolt the same as a cup head bolt? Yes. Cup head bolt is the trade and catalogue name used in Australian fastener supply for the same product called a coach bolt on site. AS 1390 (the Australian standard) calls it a cup head bolt. All three names — coach bolt, carriage bolt, cup head bolt — refer to the same fastener with the same dimensions and specifications. Do you need to pre-drill for a coach bolt? Yes. Drill a clearance hole through all members using a bit 0.5–1mm larger than the bolt shank: M6 = 6.5mm, M8 = 8.5mm, M10 = 10.5mm, M12 = 13mm, M16 = 17mm. The square neck does not self-drill — it seats into the timber surface as the nut is tightened, preventing rotation during tightening. What size drill bit do I need for a coach bolt? Drill a clearance hole 0.5–1mm larger than the bolt diameter: M6 = 6.5mm, M8 = 8.5mm, M10 = 10.5mm, M12 = 13mm, M16 = 17mm, M20 = 21mm. Always fit a flat washer under the nut to distribute clamping load across the timber grain. See our Bolt Grade Chart. What is the difference between hot-dip and electroplated galvanising on coach bolts? Hot-dip galvanised (HDG) has a thick zinc coating (45–85 microns) bonded at the molecular level — suitable for outdoor structural use, treated timber, and coastal environments. Electroplated zinc has a thin coating (5–15 microns) — adequate for indoor or sheltered use only. In outdoor and treated pine applications, always specify hot-dip galvanised. Can coach screws be used in treated pine? Yes, but only with hot-dip galvanised or stainless steel coach screws. CCA and ACQ treated pine are corrosive to electroplated zinc — electroplated coach screws in treated pine will corrode through within 2–5 years outdoors. Never use electroplated zinc fasteners in treated timber for any outdoor or structural application. Can I use coach screws instead of coach bolts for decking? For decking board-to-joist connections, coach screws are the standard and accepted practice. For primary structural connections — post-to-bearer, beam connections, or any joint specified by an engineer — check the structural drawings. If coach bolts are specified, do not substitute coach screws without written engineering approval. The load calculations are based on the specified fastener type. What is a coach bolt used for? Coach bolts are used to fasten timber to timber, timber to steel, or timber to masonry. The square shoulder under the domed head sets into the timber as you tighten the nut, preventing the bolt from rotating while you torque the nut. Common applications include timber decking, pergola posts, fence rails, structural timber frames, and gate hinges where a flush rounded head is required. Is a coach bolt the same as a carriage bolt? Yes — coach bolt is the Australian and UK term; carriage bolt is the American term. Both describe the same fastener: a domed head with a square shoulder beneath, designed to set into timber and prevent rotation under load. Sizes, threads and grades are functionally identical across the two terms. Always specify diameter, length and material when ordering. How do you install a coach bolt? Drill a clearance hole the same diameter as the bolt shank through both pieces of timber. Insert the coach bolt from the timber side and tap the head with a hammer to seat the square shoulder into the wood. Add a flat washer and nut on the opposite side and tighten. The square shoulder grips the timber and stops the bolt rotating, so you only need a spanner on the nut. What's the difference between a coach bolt and a hex bolt? A coach bolt has a domed head with a square shoulder underneath that sets into timber, with no spanner flats on the head. A hex bolt has a hexagonal head that requires a spanner or socket to hold while tightening the nut. Coach bolts work in timber where the wood grip stops rotation; hex bolts work in any material because you can hold both ends. Coach bolts give a smooth rounded finish — hex bolts leave the head proud. Coach Bolts and Coach Screws at AIMS Industrial AIMS Industrial stocks coach bolts and coach screws in metric sizes, in hot-dip galvanised mild steel and stainless steel. All fasteners meet Australian supply standards and are suitable for structural timber construction, decking, fencing, and outdoor applications. Browse Fasteners → For the matching spanner AF size on every common bolt, see our Spanner Size Chart. For screw pitch gauges, see our screw pitch gauges range stocked across Australia. AIMS Industrial stocks bolt hole castors — see the full range for trade and industrial use.
Read moreRivet Nut Guide: Sizes, Tools, Materials & How to Install
For pneumatic tools, fittings and air-line accessories, see our pneumatics range. For die grinders and air grinding tools (straight, angle, micro), see our air grinding tools range. Rivet Nut Guide: Types, Sizes, Installation & Tools (Rivnut / Nutsert) May 14, 2026 AIMS Industrial Supplies Rivet Nut Guide: Types, Sizes, Installation & Tools (Rivnut / Nutsert) Apr 27, 2026 AIMS Industrial Supplies Rivet Nut (Rivnut / Nutsert) Size + Grip Range — Quick Reference Rivet nuts (also called rivnuts, nutserts, blind threaded inserts) create a strong machine-thread fixing in thin material. Pre-drill the panel, insert the rivnut, and pull-set with a rivnut tool. The critical sizing variables are thread size, hole diameter, and grip range (panel thickness the rivnut can clamp). Thread Size Hole Diameter Standard Grip Range Pull Force (Set) M3 5.0 mm 0.5 – 3.0 mm ~3 kN M4 6.0 mm 0.5 – 3.0 mm ~5 kN M5 7.0 mm 0.5 – 3.0 mm ~7 kN M6 9.0 mm 0.5 – 3.0 mm ~10 kN M8 11.0 mm 0.5 – 3.0 mm ~15 kN M10 13.0 mm 1.0 – 4.0 mm ~22 kN M12 16.0 mm 1.5 – 4.5 mm ~30 kN Long-Grip Variant Per thread Extended (up to 12mm+) Per thread Critical: Match GRIP RANGE to total panel thickness — too thin and the rivnut spins; too thick and it won't set fully. Use the correct rivnut TOOL (different from blind rivet gun) — hand, lazy-tong, or pneumatic. Pre-drilled hole TOLERANCE matters — slightly too large = no grip; too small = stripping. AIMS stocks rivet nuts, rivet tools, air riveter tools, rivets + rivet assortment kits. What is a rivet nut? A rivet nut — also called a rivnut, nutsert, nut insert, or blind rivet nut — is a hollow, internally threaded fastener that installs into a pre-drilled hole from one side only and expands on the blind side to grip the material. Once set, it gives you a permanent threaded point in sheet metal, aluminium, fibreglass, plastic, or thin-wall tube — without needing access to the back face, and without welding. The name causes some confusion. "Rivet nut", "rivnut", "nutsert", and "nut insert" all refer to the same product. The term "nut rivet" is sometimes used in trade, though technically imprecise — the nut is the insert, not the rivet. For this guide we use "rivet nut" and "rivnut" interchangeably. The mechanism is straightforward. You load the rivnut onto a mandrel tool, push it into the hole, and squeeze or pull the tool. The mandrel pulls the threaded body upward, causing the shank to buckle outward and form a flange on the blind side. That flange clamps the material between itself and the head flange, locking the nut in place. You then thread a bolt through from the access side. When do you need a rivet nut? Use a rivnut when: The material is too thin to tap a thread directly (typically under 3–4 mm) You only have access to one side of the panel or tube The material cannot be welded (aluminium sheet, fibreglass, plastic, composite) You want a removable, bolted connection rather than a permanent pop rivet You need to add a threaded point to an existing structure without disassembly Common applications include body panels and accessories on vehicles, mounting racks and brackets on van conversions, electronics enclosures, marine fittings, furniture assembly, and sheet metal fabrication. Rivet nut vs pop rivet — what's the difference? A pop rivet (blind rivet) permanently joins two pieces of material together — the rivet itself is the fastener, and once set, it cannot be removed without drilling out. A rivet nut does the opposite: it creates a reusable threaded socket in the material so you can bolt and unbolt something repeatedly. If you want to mount a bracket that you might need to remove later — a roof rack, an instrument panel, a cable tray — a rivet nut is the right choice. If you're permanently joining two sheets of metal and removal is not required, a pop rivet is faster and cheaper. For more on blind rivets and how to choose between rivet types for permanent joining, see our Types of Rivets Guide. Types of rivet nuts Rivet nuts come in several body configurations. Choosing the right type for your application is just as important as choosing the right size — the wrong type can spin, pull out, or fail to set correctly. Round body vs hex body Round body rivet nuts have a cylindrical shank. They are the most common type and work well in steel, where the expansion force of the set fastener is enough to grip the hole wall. The limitation is torque resistance — in softer materials (aluminium, plastic, fibreglass), a round body can spin in the hole when you tighten a bolt against it. Hex body rivet nuts have a hexagonal shank that cuts into the hole wall during installation, preventing rotation. Use hex body when working in aluminium sheet, fibreglass, or any material where a smooth round body would not grip reliably. For blind-side torque resistance in demanding applications, hex body is the correct choice. Knurled / ribbed shank vs smooth shank Knurled or ribbed shank rivet nuts have longitudinal ribs along the body that bite into the hole wall as the fastener sets. They offer significantly better anti-rotation performance than smooth round-body fasteners — without requiring the exact hole shape that a hex body needs. Ribbed shanks are a good middle ground: easier to install than hex body (round hole is fine), and much more resistant to spinning than plain smooth body. Smooth shank suits standard applications in steel where hole tolerances are precise and spin-out is not a concern. Open end vs closed end Open end rivet nuts have an open thread on both the head and the blind side — they allow a bolt to pass through fully, and they are the standard type for most applications. Closed end rivet nuts are sealed at the blind end. Use closed end when: The blind side is exposed to water, dust, or contaminants A gas-tight or liquid-tight seal is required The fastener is going into a tube or sealed section Typical applications for closed end: marine fittings, outdoor enclosures, food processing equipment, and any installation where contamination from behind would be a problem. Low-profile / AET style Standard rivet nuts form a bulge flange on the blind side as they set. In some situations — installing into round tubing, shallow blind pockets, or tight assemblies — there is not enough clearance for that bulge. The low-profile (AET) style works differently: the tool separates the body into two halves, expanding the lower section radially to grip the hole wall rather than forming a back flange. This means the installed height on the blind side is minimal. Use low-profile rivet nuts for installations in square or round tubing, where you cannot create clearance for a conventional buckle flange. Floating rivet nut A floating rivet nut has a threaded insert that can shift laterally within the outer body — typically ±0.5 mm to ±1 mm in each direction. This is used when bolt hole alignment is critical but panel-to-panel tolerances are not tight enough to guarantee perfect registration. Common in automotive assembly, electrical cabinet manufacture, and electronics enclosures where multiple bolts must line up across several panels. Rivet nut sizes and grip ranges The two most important dimensions when selecting a rivet nut are the thread size and the grip range. Get either wrong and the fastener will either fail to set or will not hold adequately. Metric thread sizes Rivet nuts in Australia are predominantly metric. The most common sizes in trade and industrial use are M3 through M12. The table below gives standard dimensions and hole sizes for round-body rivet nuts — always check the manufacturer's data sheet for the specific product you are using, as dimensions vary slightly between brands. Thread Size Body OD (mm) Drill Hole (mm) Head Flange OD (mm) Typical Grip Range (mm) M3 5.0 5.1 8.0 0.5 – 2.5 M4 6.0 6.1 9.0 0.5 – 3.0 M5 7.0 7.1 11.0 0.5 – 3.0 M6 9.0 9.1 14.0 0.5 – 3.5 M8 11.0 11.1 16.0 0.5 – 4.0 M10 13.0 13.1 18.0 1.0 – 5.0 M12 16.0 16.1 22.0 1.5 – 6.0 Note: Imperial thread sizes (UNC and UNF) are available for use with older Australian equipment, American-specification vehicles, and some agricultural machinery. Common imperial rivnuts include 10-32 UNF, 1/4-20 UNC, 5/16-18 UNC, and 3/8-16 UNC. If you are working on newer Australian or European vehicles or machinery, metric is almost certainly correct. Understanding grip range Grip range is the range of material thicknesses the rivet nut is designed to clamp. A rivnut specified for a grip range of 0.5–3.0 mm will set correctly when the total panel thickness is between 0.5 mm and 3.0 mm. This matters enormously in practice: Under minimum grip: The rivet nut will not form a proper back flange. It will feel loose, may spin, and will have poor pull-out strength. Over maximum grip: The tool cannot pull the mandrel far enough to set the fastener. You will strip the mandrel or crush the body without forming a proper flange. Mid-range is best: Aim for the middle of the grip range for the most consistent set and highest pull-out force. If your panel is 1.5 mm thick, use a rivnut with a grip range centred around 1.5 mm — not one rated 0.1–3.0 mm where 1.5 mm is at one extreme. Many suppliers specify a "short grip" and "long grip" variant of each thread size — use short grip for thin sheet, long grip for thicker substrates or stacked panels. How to read a rivet nut part number Part numbers vary by manufacturer but typically encode: body material / thread size / body length / body style / shank type. For example, a part number like RN-M6-SS-H-C might decode as: Rivet Nut / M6 thread / Stainless Steel body / Hex body / Closed end. Always confirm against the manufacturer's catalogue — there is no universal standard for part number format. Rivet nut materials The body material of the rivet nut determines its corrosion resistance, strength, and compatibility with the substrate. Use the wrong material and you risk galvanic corrosion, insufficient strength, or a body that is too hard to set properly. Aluminium Aluminium rivet nuts are lightweight and corrosion-resistant, and they are the best choice for aluminium panels and structures — using an aluminium rivnut avoids the galvanic couple that would occur between a steel fastener and an aluminium substrate. They are also the right call in plastic, fibreglass, and other soft materials where the softer body deforms more easily during setting. Limitation: lower pull-out and shear strength than steel. Not suitable for high-load structural applications. Steel (zinc-plated or plain) Steel rivet nuts are the standard workhorse for general industrial, fabrication, and automotive work in steel substrates. Zinc plating provides moderate corrosion resistance — adequate for indoor or semi-sheltered environments. Not suitable for marine, food processing, or outdoor applications where sustained moisture or chemical exposure is expected. Stainless steel (304 / 316) Stainless steel rivet nuts are the right choice for marine, food-grade, and outdoor applications. Grade 316 stainless provides superior resistance to chloride corrosion (salt water). More difficult to set than aluminium or mild steel — requires a good quality tool, correctly adjusted, and slightly more force. If your tool is struggling to set stainless rivnuts, check that the mandrel stop is set correctly and that you are using the right grip range. Brass Brass rivet nuts are used primarily in plastic substrates, electrical enclosures, and electronics assemblies. Brass is soft enough to set without damaging fragile base materials, is non-magnetic, and provides good thread quality for fine threads. Also used in PCB and panel assemblies where electrical conductivity at the fastener point is required. Rivet nut tools — hand, air, and DIY methods Setting a rivet nut correctly requires the right amount of pull force, applied consistently. The tool you choose determines whether you can achieve that reliably — and how quickly. Hand rivet nut tool A hand rivet nut tool (also called a nut rivet gun) operates by squeezing the handles together, which pulls the mandrel and sets the fastener. Most hand tools accept interchangeable mandrel heads to suit different thread sizes — typically M3 through M12 are covered with a set of three to four mandrels. Hand tools are the right choice for site work, occasional use, small volumes, and anywhere compressed air is not available. Look for: A mandrel depth stop that can be adjusted per fastener size — this controls how far the mandrel pulls and prevents over-crush A knob or release mechanism to back the mandrel out of the set fastener Handles long enough to generate adequate force for M8 and M10 in steel or stainless A well-set hand tool will handle M3–M8 in aluminium and steel comfortably. For M10–M12 stainless, a pneumatic tool is a better choice if you have volume work. Pneumatic / air rivet nut tool Air-powered rivet nut tools set fasteners faster and with more consistent force than hand tools, making them the right choice for production line work, bodyshop use, or any situation where you are setting more than 20–30 rivnuts per day. They also reduce operator fatigue significantly when working with M8 and above in steel or stainless. Pneumatic tools require a compressor capable of sustaining the tool's rated CFM at the required pressure — typically 6–7 bar (90–100 psi) and 3–5 CFM. Most air rivet nut tools are also adjustable for mandrel stroke, which is critical for setting different sizes correctly. DIY method — bolt and two nuts If you do not have a rivet nut tool and need to install one or two fasteners in a pinch, the bolt-and-two-nuts method works as follows: thread a bolt through the rivet nut, then thread two nuts onto the end of the bolt and tighten them against each other (jam nut). Insert the rivet nut into the hole, hold the bolt head stationary, and tighten the inner nut with a spanner — pulling the rivet nut body up to set it. Once set, loosen and remove the bolt assembly. This method works but has limitations: it is slow, the setting force is inconsistent (difficult to judge when the fastener is properly set), and it is easy to over-crush smaller rivnuts. Use it only for one-off situations. For any volume of work, the correct tool is worth the investment. Setting the mandrel depth stop Regardless of which tool you use, setting the mandrel depth stop correctly for each fastener size is critical. The depth stop determines how far the mandrel travels on each stroke — too little travel and the fastener is under-set (weak, likely to spin); too much and you over-crush the body or strip the thread. The correct method: thread a rivet nut onto the mandrel, insert it into a scrap piece of the same material thickness you will be working in, set the fastener, and inspect the back side. The back flange should be even and fully formed, with the body not excessively crushed. Adjust the stop and repeat until the set is consistent. This takes five minutes on a scrap piece — it is not optional. How to install a rivet nut — step by step The following steps assume you are using a hand rivet nut tool. The process is the same for an air tool; the pneumatic tool handles the pull force automatically once triggered. What you will need Rivet nut tool with correct mandrel for your thread size Drill and correct drill bit (see sizing table above) Deburring tool or step drill Centre punch and hammer Rivet nuts (correct size, material, and grip range for your application) Bolt to test thread engagement after setting Safety glasses — mandatory when drilling and setting For drilling noise, consider hearing protection if working in an enclosed space or with a noisy drill. Step 1 — Mark and centre punch Mark the hole position clearly and use a centre punch to create a dimple. The punch prevents the drill bit from wandering when you start the hole, which is critical — an off-centre or oversize hole will cause the rivet nut to sit crooked or spin. Step 2 — Drill to the correct hole size Use the drill size from the manufacturer's data sheet for your specific rivet nut (refer to the sizing table above for standard dimensions). The hole should allow the rivet nut body to fit snugly — hand pressure to push it in is fine, but it should not drop through freely. Any play in the hole becomes play in the installed fastener. Drill perpendicular to the surface. A crooked hole produces a crooked fastener, which puts uneven load on the thread and the set flange. Step 3 — Deburr both sides of the hole This step is skipped constantly and causes more spinning rivnuts than any other single mistake. Drilling produces a burr on the exit face of the hole. If that burr is not removed, the rivet nut's back flange clamps against a raised ring of raised, weakened material — not the flat panel face. The result is low pull-out strength and a fastener that spins with minimal torque. Use a deburring tool, a countersink bit run lightly by hand, or the point of a step drill to clean both the entry and exit faces. The surface around the hole should be flat and smooth. Step 4 — Set the mandrel depth stop If you have not already done so, set the tool's depth stop using a scrap piece of the same material. Thread a rivet nut onto the mandrel, insert into the scrap hole, set it, and inspect the back flange. Adjust until the set is clean and consistent before moving to the actual workpiece. Step 5 — Load the rivet nut onto the mandrel Thread the rivet nut onto the mandrel until the head flange is flush against the tool nose, with the rivet nut body protruding forward. The nut should protrude far enough to engage the workpiece properly — check the manufacturer's guidance for the specific tool and fastener combination. Step 6 — Insert and set Push the rivet nut firmly into the hole so the head flange sits flat against the surface. Hold the tool perpendicular to the panel — any angle will produce an uneven back flange. Squeeze the handles fully (or trigger the air tool) until you feel the resistance change — the characteristic "click" or increase in resistance indicates the fastener has set. Do not release and re-squeeze. Setting a rivnut in two partial strokes produces an inconsistent back flange. If your hand tool requires more force than you can generate in a single stroke for larger sizes, switch to a two-handed grip or upgrade to a pneumatic tool. Step 7 — Remove the tool Turn the knob or release mechanism on the tool to back the mandrel out of the set rivet nut. On well-set fasteners this should be smooth. If the mandrel is difficult to remove, the fastener may have been over-crushed — inspect the thread before proceeding. Step 8 — Inspect and test Thread a bolt of the correct size into the installed rivet nut by hand. It should engage cleanly with no binding or cross-threading. Check that the rivet nut does not rotate when you apply moderate torque — any rotation indicates the fastener has not set correctly (see troubleshooting section below). Inspect the back flange if accessible — it should be even and fully formed with no cracks. Tips and tricks Chase the threads after setting: Run a tap of the matching size through the installed rivnut and apply a small amount of anti-seize to the bolt. Setting deformation can slightly distort the threads — a tap cleans them up and ensures smooth engagement. See our lubricant guide for anti-seize product recommendations. Practice on scrap first: Every time you start on a new material thickness or switch rivet nut size, run three to four fasteners into a scrap piece of the same material before working on the actual component. This confirms your hole size, grip range, and tool setting before you commit. Keep mandrels clean: Built-up aluminium or steel debris on the mandrel thread causes inconsistent engagement and can jam the tool. Clean mandrels with a wire brush and a drop of oil periodically. Common mistakes and troubleshooting My rivnut is spinning when I tighten the bolt Spinning after installation is the most common rivet nut failure. The causes, in order of likelihood: Hole too large: Even 0.3–0.5 mm oversize removes the interference fit between the body and the hole. The fastener has no lateral grip and spins freely. Drill a new hole in an adjacent position with the correct bit size. Deburring skipped: Back flange clamped on a burr, not the panel. The burr collapses under torque, the fastener rotates. Drill out, clean the back face, re-install. Under-set: Mandrel stop not adjusted far enough. The back flange did not fully form. Correct the tool setting, drill out the failed fastener, and re-install in a new hole. Wrong body type for material: Smooth round body in soft aluminium or plastic. Switch to ribbed shank or hex body. Grip range mismatch: Panel is thinner than the minimum grip of the fastener. The body buckled but did not clamp the panel. Use a rivnut with the correct grip range for your material thickness. If a spinning rivnut cannot be drilled out cleanly, centre punch the middle of the insert and use a left-hand twist drill bit — the left-hand rotation often winds the spinning insert out as you drill. The mandrel snapped or stripped Usually caused by over-torquing with a hand tool or using an incorrect mandrel size for the rivnut thread. Check that the mandrel threads match the rivet nut thread pitch exactly. Replace mandrels when they show wear — a worn mandrel strips easily at the thread engagement point. The rivet nut pulled through the panel Pull-through indicates the back flange area is insufficient for the load applied — either the material is too thin, too soft, or the rivnut is too small for the bolt load. Solutions: increase the rivet nut head flange size (large-flange variants available for M5–M10), use a backing washer on the blind side, or use a larger thread size. For general guidance on washers and load spreading, see our Types of Washers Guide. The thread is damaged after setting Over-crushing the rivet nut distorts the threaded body. This is most common with smaller sizes (M3, M4) where the mandrel stop was set too deep. If threads are damaged, drill out and replace. Calibrate the tool depth stop carefully on scrap before re-installing. Rivet nut vs weld nut — when to use which A weld nut is permanently welded to the base material before assembly. A rivet nut is installed after fabrication, from one side. The right choice depends on your material, access, equipment, and load requirements. Factor Rivet Nut Weld Nut Access needed One side only Both sides (for welding) Material Steel, aluminium, plastic, fibreglass, composites Steel and weldable metals only Equipment needed Drill + rivet nut tool Welder + PPE Heat distortion risk None Yes — heat affected zone around weld Removable / reworkable Yes (drill out and replace) No — permanent Pull-out strength Moderate (load-rated per size) High — structural if welded correctly Best for Retrofit, thin sheet, non-weldable materials, post-assembly fitment Structural, high-load, production line fabrication For most trade and maintenance applications — van fitouts, panel work, equipment mounting, light fabrication — a rivet nut is the faster, more flexible, and safer choice. Weld nuts are preferred in structural applications (chassis, heavy brackets, high-vibration environments) where the permanent bond and higher load rating justify the welding step. For a full rundown on nut types including weld nuts, cage nuts, and flange nuts, see our Types of Nuts Guide. Shop rivet nuts and tools at AIMS Industrial AIMS Industrial stocks a range of rivet nuts across metric thread sizes M3 to M12 in aluminium, steel, and stainless steel — including round body, hex body, and closed-end variants. We also carry rivet nut tools to suit everything from occasional DIY fitments to regular trade use. Browse our full fasteners range — rivet nuts, bolts, nuts, washers, and more Shop rivet nut tools — hand tools and accessories Need advice on the right size, material, or tool for your job? Contact our team on (02) 9773 0122 or email sales@aimsindustrial.com.au. Frequently asked questions — rivet nuts and rivnuts What is the difference between a rivet nut and a nutsert? Rivet nut and nutsert are two names for exactly the same product. Other common names include rivnut, nut insert, and blind rivet nut. All refer to a hollow internally threaded fastener that installs into a pre-drilled hole from one side and expands on the blind side to create a permanent threaded anchor point. Are rivets and rivnuts the same thing? No. A standard pop rivet (blind rivet) permanently joins two pieces of material together — it has no internal thread and cannot be used with a bolt. A rivnut (rivet nut) creates a reusable threaded socket in the material so you can bolt and unbolt something repeatedly. They share a similar installation principle but are completely different fasteners serving different purposes. What are the disadvantages of using rivnuts? The main disadvantages are: lower pull-out strength compared to welded nuts; susceptibility to spinning if incorrectly installed or if the hole is oversized; requirement for precise hole sizing (even 0.5 mm oversize can cause failure); and the need for a specific installation tool for consistent results. They are also not suitable for very high-load structural applications where weld nuts are preferred. What is the difference between open end and closed end rivet nuts? Open end rivet nuts are unsealed at the blind side — a bolt can pass through fully, and they are the standard type for most applications. Closed end rivet nuts are sealed at the blind end, blocking water, dust, and contaminants from passing through. Use closed end for marine, outdoor, food processing, or any environment where contamination from the blind side is a concern. Why does my rivnut keep spinning? Spinning is almost always caused by one of four things: the drilled hole is slightly too large (even 0.3–0.5 mm oversize causes loss of grip); the burr on the back face of the hole was not removed before installation (the flange clamps on the burr, not the panel); the fastener was under-set because the tool depth stop was not adjusted correctly; or the wrong body type was used (a smooth round body in soft aluminium or plastic will spin — switch to ribbed shank or hex body). What size hole do I need for a rivet nut? The correct hole size is typically 0.1 mm larger than the body OD of the rivet nut — just enough clearance to push the body in by hand without it dropping through. For common metric sizes: M5 requires approximately a 7.1 mm hole, M6 requires 9.1 mm, M8 requires 11.1 mm, and M10 requires 13.1 mm. Always check the manufacturer's data sheet for the specific product, as dimensions vary between brands. What grip range do I need? The grip range must match your panel thickness. Measure the total thickness of the material you are fastening into and select a rivet nut with a grip range that includes that thickness — ideally near the middle of the range rather than at the extremes. A rivnut specified for 0.5–3.0 mm will not set correctly in a 0.1 mm panel or a 4 mm panel. Most suppliers offer short grip and long grip variants in each thread size. Do I need a special tool to install rivet nuts? A dedicated rivet nut tool is strongly recommended for consistent results. Hand rivet nut tools start from around AUD $50–80 and handle M3–M10 in aluminium and steel. Pneumatic tools suit higher-volume work and M8–M12 in stainless. In an emergency, a bolt and two jam nuts can be used (thread the assembly through the rivnut, insert into the hole, hold the bolt head and tighten the inner nut to draw the body up) — but setting force is inconsistent and it is easy to over-crush smaller sizes. Can rivet nuts be used in aluminium? Yes. When installing into aluminium substrate, use aluminium body rivet nuts to avoid galvanic corrosion between dissimilar metals. Hex body or ribbed shank is strongly recommended for aluminium substrate — smooth round-body rivnuts can spin in the softer material. Ensure hole sizing is precise, as aluminium deforms more easily than steel and an oversized hole gives even less grip. Can rivet nuts be used in plastic or fibreglass? Yes, with the right selection. Use aluminium or brass body rivet nuts in plastic and fibreglass — steel is too hard and can crack brittle substrates during setting. Hex body or large-flange variants distribute load over a larger area and reduce the risk of pull-through in lower-strength materials. Set carefully with controlled force — plastic and fibreglass can crack if the mandrel stop is too deep. What is the difference between a round body and hex body rivet nut? A round body rivet nut has a cylindrical shank — it relies on the expansion force of the set flange to resist rotation. A hex body rivet nut has a hexagonal shank that cuts into the hole wall during installation, providing mechanical anti-rotation resistance. Use round body in steel where interference fit is reliable. Use hex body in aluminium, plastic, fibreglass, and any material where a smooth body would spin under bolt torque. When should I use a rivet nut instead of a weld nut? Use a rivet nut when: you only have access to one side of the panel; the material cannot be welded (aluminium sheet, fibreglass, plastic, composite); you want a removable or reworkable fastener; welding equipment is unavailable; or heat distortion from welding would be a problem. Use a weld nut for permanent, high-load structural joints in steel where welding equipment is available and a stronger permanent connection is required. Share: Share on Facebook Share on X Pin on Pinterest Previous Post Linear Bearing Guide: Types, Sizes & How to Choose Next Post Chain Lube Guide: Wet, Dry, Wax & Industrial Types Explained What is a rivnut used for? Rivnuts (rivet nuts) provide a threaded mounting point in thin sheet material where you can only access one side and where welding a nut isn't practical. Common applications include automotive panels, marine hatches, aluminium signage, electrical enclosures, tube frames and HVAC ductwork. They give you a strong reusable thread in a single sheet without the need for backing nuts or weld-on bosses. How does a rivnut work? The rivnut is a threaded steel or aluminium tube with an enlarged head at one end. It's installed using a rivnut tool that grips the internal thread and pulls the body upward, collapsing it into a flange that clamps the sheet between the head and the deformed body. The internal thread is left intact for fitting bolts. Once installed, the rivnut provides a permanent threaded mounting point. What's the difference between a rivet and a rivnut? A standard rivet creates a permanent join between sheets of material with no thread — once installed it can't accept a bolt. A rivnut is a threaded fastener installed in a single sheet that provides a threaded hole for a bolt to engage. Standard rivets join two pieces; rivnuts add threaded mounting points to one piece. Both are installed from one side of the sheet. What size rivnut do I need? Rivnuts are sized by the bolt thread they accept — M3, M4, M5, M6, M8, M10, M12 are common in metric, plus imperial equivalents. Match the rivnut to the bolt you'll install through it. Match the grip range to the thickness of the sheet you're installing into — too thin and the rivnut won't clamp properly; too thick and it won't deform fully. Most rivnuts have a stamped grip range on the head. 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Washers are among the most commonly used fastening components in Australian industry — and among the most poorly understood. A washer is not just a.
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