Product Guides
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.A nyloc nut and a threadlocker solve the same problem — vibration loosening — by different means: one mechanically, one chemically. They can be used together on critical joints, or a threadlocker on a plain hex nut can do the job on its own where a nyloc isn't practical. See our Loctite Threadlocker Guide for grade selection.
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When this article says "nuts," it means fastener nuts — the threaded components that pair with bolts, studs, and threaded rod to clamp assemblies together. There are more types than most people realise, and choosing the wrong one costs time, causes failures, and occasionally causes injury. This guide covers every nut type you will encounter in Australian trade and industrial work: what each one is, how it works, when to use it, and what class to specify for the bolt you are pairing it with. Bookmark our Engineering Reference Charts hub for related sizing tables, conversion charts and Australian standard references across 9 topic clusters. What Is a Nut and How Does It Work? A nut is an internally threaded fastener that mates with an externally threaded bolt, screw, or stud. When tightened, the nut bears against the surface of the clamped material on one side while the bolt head bears against the other. The act of tightening stretches the bolt very slightly — this elastic elongation (bolt tension, or preload) is what creates the clamping force that holds the joint together. Friction between the bearing faces and the bolt-thread/nut-thread interface resists loosening under normal service loads. The thread form defines geometry: metric nuts follow the ISO thread standard (60° thread angle, pitch in mm); imperial nuts follow either Unified National (UN, 60°) or Whitworth (BSW, 55°) standards. Metric and imperial threads are not interchangeable — forcing an imperial nut onto a metric bolt (or vice versa) at a nominally similar diameter will damage threads or give a false sense of security on a mismatched pair. Thread engagement length matters. A nut that is too thin may strip before developing the bolt's full proof load. This is why thin nuts (half nuts, jam nuts) are not direct substitutes for standard-height hex nuts in structural applications. The standard height for a metric hex nut is approximately 0.8 times the nominal bolt diameter — enough engagement to develop the bolt's rated proof load without stripping the nut threads. For tightening nuts on hex bolts, open-end, ring, and combination spanners are the standard tools — our Types of Spanners guide covers selection and sizing. For production work and accessible bolting, a socket set driven by a ratchet or impact driver is faster. For critical applications with a specified torque, a torque wrench is required. The nut drives the bolt tension, and the torque applied determines the resulting preload — both under-torquing (loose joint) and over-torquing (yielded bolt) are failure modes. Hex Nut (Full Nut) The hex nut — also called a "full nut" in Australian trade — is the baseline. Six flat faces accept a spanner or socket, the standard internal thread height develops full engagement with the paired bolt, and nothing else about the design is optimised for anything in particular. It is the correct choice for any application where a specific nut feature (locking, capping, extension, quick-release) is not required. In Australia, hex nuts to metric dimensions follow AS 1112.1 and are specified by property class: Class 5, 6, 8, 10, or 12. The most common stocked class is Class 6, which pairs with 6.8 and 8.8 grade bolts across the majority of general industrial and construction applications. Class 8 hex nuts are specified for high-tensile 8.8 and 10.9 bolt assemblies where the nut must develop the full proof load of the bolt. (The nut-to-bolt matching rules are covered in detail in the Property Classes section below.) Hex nuts are available in standard and wide-series (larger across-flats dimension for greater bearing area), and in normal and thin (half-nut) heights. Standard-height hex nuts are stamped on the bearing face or across the flats with the property class number. A hex nut with no markings is generally a Class 4.6 or equivalent mild steel — not a substitute for a marked Class 6 or Class 8 in a structural application. Finishes: plain (self-colour, mild carbon steel), zinc-plated (BZP), hot-dip galvanised (HDG), and stainless steel. For guidance on when stainless or galvanised finishes are needed, see our Stainless Steel Fastener Grades guide. Thin Nut (Jam Nut / Half Nut) A thin nut is approximately half the height of a standard hex nut. It is called a "jam nut" or "half nut" when used in a two-nut locking assembly; the trade and catalogue term in Australia is typically "thin nut." The two legitimate uses of thin nuts are: first, as part of a jam-nut pair — two nuts on the same thread, tightened against each other. The method is to fit a thin nut first, partially tighten it, then fit a full nut on top and tighten the full nut hard against the thin nut. The reaction load between the two creates a locking effect. Correctly executed, this is a reliable locking method used in adjustable mechanical assemblies (valve adjusters, turnbuckles, jig fixtures). Second, in applications where the available thread protrusion is insufficient for a full-height nut, a thin nut may fit where a standard nut will not. The critical misuse to avoid: substituting a thin nut for a full nut in a single-nut application because a full nut is unavailable or does not fit. A thin nut used alone has significantly lower proof load than a full nut of the same class — the reduced thread engagement means the nut threads will strip at a lower force than the bolt will yield. This is a joint failure mechanism, not a design choice. Nyloc Nut (Nylon Insert Lock Nut) The nyloc nut is the most commonly specified lock nut in Australian trade and industrial work. It has a standard hex body with a full-height thread section below, and a nylon insert ring pressed into the top of the nut body. The nylon insert has no pre-formed thread — when the nut is driven down a bolt, the bolt thread cuts into the nylon and the compressed nylon grips the thread flanks under spring pressure. This interference creates friction that resists the nut backing off under vibration or dynamic load. The nyloc nut provides locking through friction only, not through mechanical interlock. The friction is reliable and effective within its rated operating conditions, but it can be overcome by sufficient axial load or loss of the nylon's elastic properties. Two conditions degrade nyloc performance significantly: Temperature: Nylon retains its elastic properties between −40°C and approximately +120°C. Above 120°C, the nylon softens and loses its grip on the thread flanks — the nut is no longer effectively locked. Below −40°C, nylon becomes brittle and may crack during installation. Nyloc nuts must not be used near heat sources: exhaust manifolds, flue connections, kilns, ovens, furnace components, or any assembly that regularly reaches above 100°C in service. The correct alternative for high-temperature applications is a prevailing torque all-metal lock nut or a castle nut with split pin. Reusability: Each time a nyloc nut is removed and reinstalled, the nylon insert undergoes additional deformation. Locking effectiveness diminishes with each cycle. The general guideline is that a nyloc nut may be reused if: the nut turns freely by hand when run down the thread (before the nylon engages), the nylon insert is intact with no cracking or deformation, and the thread is undamaged. In critical applications — structural bolting, load-bearing connections, anything where progressive loosening could cause injury — replace the nyloc nut on every disassembly. Nyloc nuts are available in Class 04 (a thin-body variant, lower profile), Class 6, Class 8, and Class 10. The class rating refers to the proof load of the metal body — the nut must still be matched to the bolt grade for strength. A Class 6 nyloc nut on a 10.9 bolt gives you nyloc locking action but insufficient thread engagement strength — the nut body will strip before the bolt yields under full load. Match property class to bolt grade. DIN 985 specifies the thin-body (half-height) nyloc; DIN 982 specifies the regular-height nyloc. Regular-height nylocs are the standard stock item in AU. For stainless nyloc nuts, the nylon insert is standard nylon — the limiting temperature remains +120°C regardless of the stainless body material. Shop nylon lock nuts: AIMS Nylon Lock Nuts For the full reference — DIN 985 vs DIN 982, the 120°C temperature ceiling explained, reuse decision rules, all-metal Stover and threadlocker alternatives, and matching nyloc grade to bolt grade — see our dedicated Nyloc Nut Guide. Prevailing Torque Nut (All-Metal Lock Nut) A prevailing torque nut achieves vibration resistance without nylon. Locking is built into the metal geometry of the nut itself — either through a distorted or elliptical top section, a tri-lobular thread form in the upper portion, or a section of thread that is slightly out-of-round relative to the bolt thread. When the nut is driven past the undistorted section and reaches the prevailing torque zone, the interference between the nut's deformed metal and the bolt thread creates resistive torque that must be overcome for the nut to turn in either direction. The key advantage over nyloc is temperature resistance. All-metal prevailing torque nuts can operate at temperatures far beyond the nylon limit — typically 200°C or higher depending on material, making them the correct choice for exhaust systems, near-engine applications, kiln equipment, and any assembly where service temperature exceeds the nyloc limit. The trade-off is higher installation torque — more force is required to drive a prevailing torque nut down the thread compared to a standard nut, because the interference is present throughout the thread engagement rather than only at the insert zone. This makes them less convenient for high-volume assembly. They are also generally more expensive than nyloc nuts of the same size. Common types: Philidas nut (distorted thread), Stover nut (conical top section), and elliptical-profile lock nuts. All are classed under the prevailing torque nut category in AS/NZS and ISO standards. Flange Nut A flange nut has a standard hex body with an integrated circular flange on the bearing face. The flange acts as a captive washer: it distributes the bearing face load across a larger contact area than the nut face alone, reducing surface stress on the clamped material. Because the washer is integral, there is no risk of forgetting or losing a separate washer during assembly. The non-serrated (smooth) flange nut does not bite into the mating surface. This makes it appropriate for applications where surface damage is unacceptable: painted surfaces, anodised aluminium, coated panels, and soft substrates. It is not a locking nut in the vibration-resistance sense — the smooth flange increases bearing area but does not significantly increase rotational resistance beyond that of a standard hex nut with a washer. Flange nuts are common in automotive applications (particularly in suspension and exhaust systems, where the broader bearing face compensates for oversized clearance holes), in machinery assembly where a separate washer step is to be eliminated, and in pipe and structural flange connections. Serrated Flange Nut The serrated flange nut adds radial or angular serrations to the bearing face of the flange. When tightened, these serrations bite into the mating surface, creating a mechanical interlock that resists rotation. The serrations work like a one-way ratchet against the surface — under vibration, the tendency to loosen is resisted by the serrations re-engaging the surface marks they have already created. This makes the serrated flange nut a legitimate locking nut, not just a load-distributing nut. It is widely used in automotive chassis assembly, engine bay components, and machinery where vibration is present and a separate locking method (nyloc, thread locker) is inconvenient or inappropriate. The limitation is the surface contact requirement. Serrated flange nuts should not be used on: plated or coated surfaces where the coating provides corrosion protection (the serrations cut through the coating); anodised aluminium (serrations destroy the anodise layer); painted cosmetic surfaces (visible scoring); soft materials like plastic or composite panels (serrations can crack or over-stress the substrate). For these surfaces, a smooth flange nut with a separate spring or star washer provides locking without destructive serration. Wing Nut The wing nut has two large flat wings projecting radially from the nut body, providing enough lever arm for the nut to be tightened and loosened by hand without any tools. It is the correct choice where frequent manual adjustment or quick release is needed and where vibration or high torque loads are not present. Common Australian applications: battery terminal nuts (positive and negative clamps), dust extraction hose couplings, machine cover panels requiring routine access, air filter canisters, temporary assembly work, and test fixtures. The wing nut is the right answer to the question "how do I fasten this so I can undo it by hand in thirty seconds?" For the full reference covering DIN 315 vs DIN 315 A, stamped vs cold-formed vs forged, sizing M3 to M24, and material selection, see our Wing Nut Guide. Wing nuts are not appropriate for structural load, vibration environments, or any application where the nut may be contacted by a rotating component or moving part. The projecting wings are a snagging and entanglement hazard in rotating machinery — the same prohibition that applies to gloves at rotating equipment applies here. Wing nuts in machinery enclosures should only be used on panels that are always stationary when the machine is running. Shop wing nuts: AIMS Wing Nuts Castle Nut (Castellated Nut) A castle nut has a standard hex body below, topped by a cylindrical crown section with slots machined through it at regular intervals around the circumference. In use, a split pin (the Australian term for what Americans call a cotter pin) is passed through two opposing slots in the crown and through a cross-hole drilled through the bolt or stud. The split pin's legs are bent outward on the other side to prevent withdrawal. The result is a positive mechanical lock: the nut physically cannot rotate because the split pin bridges the nut slots and the bolt hole. This positive lock does not rely on friction, nylon properties, metal deformation, or any mechanism that degrades over time and temperature. The castle nut with split pin will hold as long as the split pin is intact and the bolt cross-hole is undamaged. This is why it is the specified fastening method in safety-critical, low-torque, or high-consequence applications where gradual loosening would be catastrophic. The primary AU applications are trailer wheel hub bearings, boat trailer wheel bearings, and light vehicle front wheel hub assemblies where a tapered roller bearing is retained by a castle nut running on the stub axle. The installation procedure is specific: tighten to specified torque to seat the bearing, then back off to the nearest slot that aligns with the cross-hole, insert the split pin, and bend. The nut is deliberately not torqued to maximum — the bearing requires controlled end-float, and over-tightening destroys the bearing rapidly. Other applications: tow hitch pin retention, steering linkage rod ends, suspension pivot pins, and any pin joint where vibration loosening would cause component separation. Castle nut vs slotted nut: These are sometimes used interchangeably, but there is a difference. A castle nut has a distinct cylindrical crown section above the hex — the slots are only in the crown, and the hex below is full height. A slotted nut has slots machined through the full hex height, with no separate crown section. The castle nut's crown geometry confines the split pin closer to the nut axis, which some engineers prefer for positive retention. In practice, both work correctly with a split pin through matching bolt cross-holes. Dome Nut (Acorn Nut / Cap Nut) A dome nut — also called an acorn nut or cap nut — has a standard hex body below and a closed domed cap at the top. The dome encloses the bolt thread end, protecting it from corrosion, impact damage, or contamination. The smooth domed exterior also provides a clean, finished appearance and eliminates the exposed sharp thread end that can cause cuts and snagging. Dome nuts are used where: the thread end will be exposed to the weather or corrosive atmosphere; the assembly is in a location where contact with a sharp thread end is a safety concern (handrail fittings, public furniture, playground equipment, marine fixtures); or a finished appearance is required (consumer products, display fittings, architectural metalwork). The thread depth inside the dome is limited — the nut can only accept a bolt that protrudes a specific number of threads into the dome cavity. Bolts that protrude too far cannot be fully tightened (the bolt end bottoms out in the dome before the nut clamps the joint). Always check thread engagement against the dome nut's internal cavity depth when selecting size. Available in stainless steel, zinc-plated steel, and brass. Stainless dome nuts are a common choice for outdoor handrail and balustrade assemblies in coastal environments where both corrosion resistance and appearance matter. Shop dome nuts: AIMS Dome Nuts Coupling Nut (Extension Nut) A coupling nut is a long hex nut — typically three times the length of a standard hex nut at the same diameter — used to join two lengths of threaded rod end-to-end, or to thread onto a stud and extend it. The long body provides thread engagement with both male thread ends simultaneously, and the hex exterior accepts a spanner for tightening. The most common application in Australian construction and industrial work is suspended ceiling systems: threaded rod is hung from the structural slab, coupling nuts are used to extend the rod downward to the ceiling grid level when a single rod length is insufficient. Coupling nuts are also used in pipe support hangers, conveyor structure, industrial platforms, and any application involving long threaded rod assemblies. Coupling nuts are available in metric and imperial thread forms. Metric DIN 6334 is the standard specification. Full-thread coupling nuts accept the same thread throughout their length — both rods must be the same diameter and pitch. Reducing coupling nuts accept different sizes at each end — useful for thread size transitions. T-Nut (Tee Nut) A T-nut (tee nut) consists of a threaded barrel (the nut body) with a flat circular or square flange at one end and two or more sharp prongs projecting from the flange in the same axial direction as the barrel. Installation requires a pre-drilled hole in a timber or sheet material substrate. The barrel is inserted into the hole from one face; the prongs are driven into the surrounding timber surface (or the flange is seated against the substrate face) to anchor the nut rotationally; a bolt from the opposite face drives into the barrel and draws a cap or cover tight, pulling the flange flush against the hole face. T-nuts provide a reusable threaded insert in wood, MDF, and similar substrates — materials that cannot themselves hold adequate thread engagement for repeated assembly and disassembly. They are standard in: furniture joinery (bed frames, shelf units, table aprons), woodworking jig boards and fixture tables, architectural joinery, and flat-pack cabinet construction where a durable threaded point is required at a specific location. T-nuts are not used in metal-to-metal assemblies — they are a wood/sheet fastener. For a captive threaded insert in metal sheet, the weld nut or a threaded insert insert (helicoil, rivet nut) is the correct choice. Barrel Nut (Furniture Connector Nut) A barrel nut is a cylindrical (not hexagonal) nut with a threaded cross-hole through its diameter rather than through its length. Installation requires two holes: one through-hole for the connecting bolt (perpendicular to the joint face) and one cylindrical recess hole (parallel to the joint face) into which the barrel body sits. The bolt passes through the panel or timber, enters the barrel's cross-hole, and is tightened — drawing the joint together. The barrel nut is completely enclosed in its recess and invisible in the assembled joint. Barrel nuts are the standard concealed fastener in flat-pack and ready-to-assemble (RTA) furniture: beds, bookshelves, flat-pack wardrobes, and office furniture. They are also used in timber frame construction where a clean face is required, in exhibition stand joinery, and in modular equipment structures. The concealed installation means no protruding fastener heads on any face of the joint. Most commonly encountered in M6 and M8 metric thread sizes. Usually supplied in bright zinc or nickel-plated steel for furniture applications. The bolt that engages the barrel nut typically has a pan or button head — recessed in the through-hole face. Weld Nut A weld nut is a nut specifically designed for welding to a parent material — typically a steel panel or structural member — to create a captive threaded point. Once welded, a bolt can be fastened from the accessible side only, without any nut access from behind. This is essential on thin panels, hollow sections, and assembled structures where the nut side is enclosed. The most common types are the square projection weld nut (DIN 928) and the hex flange weld nut. Projection weld nuts have small raised projections on the bearing face that concentrate the welding current and create localised weld points. Flange weld nuts have a broad flange that seats flush against the panel surface and are typically MIG or spot-welded around the flange perimeter. Weld nuts are standard in automotive body manufacture, equipment frames, electrical enclosures, and any sheet metal assembly where the blind-side access problem exists. The parent material must be weldable steel — weld nuts cannot be used on aluminium panels with standard welding, stainless without appropriate welding procedure, or galvanised sheet (the zinc coating releases toxic fumes and prevents a clean weld). Nut Property Classes — Class 5, 6, 8, 10, 12 Explained The property class stamped on a metric nut is a mechanical performance designation, not a material specification. It tells you the proof load the nut can sustain without stripping, which determines what bolt grade the nut can be paired with to develop the bolt's full rated load. The relevant Australian standard is AS 1112 (hex nuts) and AS/NZS 4291.2 (mechanical properties), which aligns with ISO 898-2. The property class system for nuts differs from the bolt grade marking system — bolt grades are two numbers separated by a decimal point (4.6, 8.8, 10.9); nut classes are single numbers (5, 6, 8, 10, 12) or two-digit codes (04 for thin nuts). Do not confuse the nut class number with the bolt grade number even where they appear similar. Class 5 General commercial grade. Used with Class 4.6 and 5.6 bolts. Not marked with a class number on most commercially available nuts — unmarked hex nuts in general trade supply are typically equivalent to Class 5 or lower. Not appropriate for structural applications or high-tensile bolt assemblies. Class 6 The standard general-purpose nut class in Australian supply. Matched to 8.8 bolts in general mechanical and construction applications. This is the most commonly stocked nut class in AU. A Class 6 hex nut is marked "6" on the face or flats. When a drawing specifies "hex nut, class 6" this is what is ordered. Class 8 High-tensile nut. Required when paired with 8.8 bolts in structural applications, and when paired with 10.9 bolts in general applications. Marked "8." Available in standard hex and in nyloc variants (Class 8 nyloc). The nut must be able to develop the bolt's full proof load — pairing an 8.8 bolt with a Class 6 nut in a structural joint risks thread stripping at the nut before the bolt yields. Class 10 Matched to 10.9 bolts. Marked "10." Used in high-strength structural connections, machinery, and critical fastened joints. Less common in general supply — typically a special-order or heavy-industrial item. Class 12 For 12.9 bolts. The highest standard property class for commercial metric nuts. Marked "12." Specialist application — precision machinery, tooling, critical fastened joints. Not a standard stock item at most AU suppliers. Class 04 The thin (half-height) nyloc nut class. The "0" prefix denotes thin height. Used in applications where the standard nyloc height does not fit. Lower proof load than full-height nyloc — verify thread engagement is adequate for the application. For full bolt grade markings and the matching of bolt grades to application requirements, see our Bolt Grade Chart guide. Matching Nut Class to Bolt Grade The fundamental rule: the nut must be capable of sustaining at least the full proof load of the bolt it is paired with, without stripping. Using an under-classed nut does not reduce the bolt's rated tension capacity — the bolt will attempt to develop its full proof load during tightening, and the under-classed nut threads will strip first. The joint fails in a way that is not visible from outside the assembly. Bolt Grade (metric) Minimum Nut Class Typical application 4.6 Class 5 General structural steel, light fabrication 5.6 Class 5 General structural 6.8 Class 6 General mechanical, machinery 8.8 Class 8 High-tensile structural, heavy machinery 10.9 Class 10 Critical structural, high-load connections 12.9 Class 12 Precision machinery, critical high-strength joints Note for imperial fasteners: the SAE Grade system (Grade 2, 5, 8) does not correspond directly to the ISO property class system. Grade 2 nuts pair with Grade 2 and Grade 5 bolts; Grade 5 nuts pair with Grade 5 bolts; Grade 8 nuts pair with Grade 8 bolts. Do not cross-reference SAE grades and ISO property classes as if they are equivalent. For more on identifying bolt grades and markings, see our Bolt Grade Chart. Which Locking Nut Should You Use? The choice between locking nut types comes down to four factors: operating temperature, whether surface marking is acceptable, whether the nut will be removed and reinstalled, and whether a positive mechanical lock (castle nut) is required by the application or relevant standard. Locking method Max temp Surface marking Reusable? Positive lock? Best for Nyloc nut +120°C None Limited No General vibration resistance, most industrial applications below 120°C Serrated flange nut +300°C+ Yes — bites surface Yes (new surface marks) No Automotive, chassis, exhaust, unpainted structural steel Prevailing torque (all-metal) +200°C+ None Yes (limited cycles) No High-temperature applications, exhaust, near-engine components Castle nut + split pin Unlimited None Yes (replace split pin) Yes Wheel hub bearings, safety-critical joints, regulatory requirement Thin nut + full nut (jam pair) Unlimited None Yes No (friction) Adjustable assemblies, turnbuckles, jig fixtures Shop lock nuts: AIMS Lock Nuts | Hex Lock Nuts Quick Selection Guide Application Recommended nut Key reason General bolted assembly, structural steel Hex nut (Class 6 or 8) Standard, correct class for bolt grade Vibration environment, below 120°C Nyloc nut Reliable friction locking, widely available Vibration, above 120°C or near heat source Prevailing torque nut All-metal locking, no nylon temperature limit Automotive chassis, unpainted structural steel Serrated flange nut Bites surface, vibration resistance, no separate washer Wheel hub bearings, trailer axles Castle nut + split pin Positive mechanical lock, standard AU trailer requirement Quick hand-release (battery terminals, covers) Wing nut No tools required, fast on/off Exposed thread end protection (outdoor, cosmetic) Dome nut Encloses thread, corrosion and injury protection Joining two lengths of threaded rod Coupling nut Full thread engagement both rods, hex drive Timber/MDF threaded insert (furniture, jigs) T-nut Provides reusable thread in non-metallic substrate Concealed joint in furniture or timber frame Barrel nut Invisible when assembled, clean face on all panels Thin panel, bolt access one side only Weld nut Captive thread, no back-access required Locking two nuts against each other Thin nut + full nut pair Jam nut locking, adjustable assemblies Coated or soft surface, load distribution needed Smooth flange nut Wide bearing face, no surface damage Frequently Asked Questions What is the difference between a nyloc nut and a standard hex nut? A standard hex nut relies on friction between the bolt thread flanks and nut thread flanks to resist loosening. Under vibration or dynamic load, this friction can be overcome progressively — the nut backs off. A nyloc nut adds a nylon insert ring at the top of the nut body. When the nut is tightened, the bolt thread deforms the nylon, and the nylon grips the thread under spring pressure. This additional friction significantly increases resistance to vibration loosening. The trade-off is a temperature limit of approximately +120°C (above which the nylon softens and loses its grip), reduced effectiveness after multiple removal and reinstallation cycles, and slightly higher installation torque. Can I reuse a nyloc nut? Yes, with limitations. Each time a nyloc nut is removed and reinstalled, the nylon insert undergoes additional deformation and its locking effectiveness diminishes. For non-critical applications, a nyloc nut that shows no cracking, runs freely on the thread before the nylon engages, and has an intact insert can be reused. For critical applications — structural connections, load-bearing assemblies, safety-related joints — replace the nyloc nut on every disassembly. A nyloc nut costs a fraction of the labour involved in disassembly; replacing it is the correct practice in critical applications. What is a castle nut and when should I use one? A castle nut has a cylindrical crown with slots above its standard hex body. A split pin passes through the slots and a cross-hole in the bolt or axle, physically preventing the nut from rotating. Use a castle nut wherever a positive mechanical lock is required: trailer wheel hub bearings, boat trailer axles, steering linkage pins, and tow hitch retaining nuts. The positive lock does not rely on friction or nylon — it is as secure as the split pin is intact. The paired bolt or stud must have a pre-drilled cross-hole for the split pin to pass through. Nyloc vs serrated flange nut — which is better for vibration? Both are effective, but for different conditions. Nyloc nuts rely on nylon friction — effective below 120°C, no surface damage, limited reusability. Serrated flange nuts rely on serrations biting into the mating surface — effective at high temperatures, no nylon limit, but the serrations mark the surface and are unsuitable for coated, painted, or soft substrates. For general indoor machinery below 120°C, a nyloc is simpler and neater. For automotive chassis, unpainted structural steel, or applications above the nyloc temperature limit, the serrated flange nut is the better choice. What property class nut should I use with an 8.8 bolt? Class 8. An 8.8 bolt in a structural application requires a Class 8 nut to develop the bolt's full proof load without the nut stripping. In non-structural or general-purpose applications, a Class 6 nut is sometimes used with 8.8 bolts, but this is only appropriate where the assembly torque is well below the nut's stripping point. For any bolted joint where the bolt is torqued to specification, the nut must match or exceed the required class. The nut marking is stamped on the bearing face or flats — "8" denotes Class 8. What is the difference between property class and grade for nuts? Property class is the ISO/metric designation for nut strength (Class 5, 6, 8, 10, 12) used in Australia under AS 1112. Grade is the SAE/imperial designation (Grade 2, 5, 8) used on American-specification fasteners. They are different systems and cannot be directly cross-referenced numerically. A metric Class 8 nut and an imperial Grade 8 nut are not equivalent — they have different mechanical properties, thread forms, and dimensional standards. When mixing metric and imperial in older plant or equipment, identify the actual thread form before selecting replacement nuts. Can nyloc nuts be used at high temperatures? No — not above approximately +120°C. The nylon insert softens above this temperature and loses its grip on the bolt thread. The nut becomes a standard hex nut without effective locking. For applications above 120°C — near exhaust systems, in ovens, kilns, near welding, or on industrial process equipment — use a prevailing torque all-metal lock nut, a serrated flange nut, or a castle nut with split pin. The operating temperature of the assembly determines which locking method is appropriate, not just the ambient air temperature. What is a prevailing torque nut? A prevailing torque nut achieves vibration resistance through the metal geometry of the nut itself — a distorted thread, elliptical profile, or tri-lobular form in the upper thread section creates interference with the bolt thread throughout installation and removal. No nylon is involved, so there is no temperature limit from the insert. The nut provides resistive torque against both tightening and loosening — the torque required to drive it exceeds that of a standard nut. This makes it the correct replacement for a nyloc nut in any application where service temperatures exceed the nyloc limit. What is a coupling nut used for? A coupling nut is used to join two male-threaded components end-to-end — most commonly two lengths of threaded rod, or a stud and a threaded rod. It is a long hex nut (approximately three times the standard length) that threads onto both components simultaneously, with its hex exterior accepting a spanner for tightening. The most common application in Australian construction is suspended ceiling systems, where coupling nuts extend threaded rod hangers to the required ceiling height. They are also used in pipe support systems, conveyor structures, and industrial frame assemblies involving long threaded rod runs. What is the difference between a dome nut and a cap nut? Nothing — they are the same fastener, referred to by different names. The standard catalogue term in Australian supply is "dome nut." The term "cap nut" or "acorn nut" (from the shape resemblance) is also used, particularly in older catalogues and American technical literature. All refer to the hexagonal nut with a closed domed top that covers and protects the exposed bolt thread end. When ordering, dome nut and cap nut will return the same product category. What does "full nut" mean? In Australian trade, "full nut" means a standard-height hex nut — specifically, a hex nut of the normal (non-thin) height as specified in AS 1112.1. The term distinguishes the standard nut from a thin nut (half nut, jam nut), which is approximately half the height. A "full nut" provides full thread engagement to develop the bolt's proof load. When a trade counter asks if you need a "full nut or a thin nut," this is the distinction being made. Which nuts can be used in outdoor or corrosive environments? Stainless steel (304 or 316) is the correct material for nuts exposed to weather, moisture, salt spray, or corrosive process environments. 316 stainless is specified for coastal and marine environments and anywhere chloride exposure is expected. Hot-dip galvanised (HDG) hex nuts are appropriate for structural outdoor applications — HDG provides thick zinc coating that gives extended protection in most atmospheric environments but is not appropriate for immersion or chemical exposure. Zinc-plated (BZP) nuts provide minimal corrosion protection and are not suitable for exposed outdoor use. For full guidance on finishes, see our Stainless Steel Fastener Grades guide. Shop Nuts at AIMS Industrial AIMS Industrial stocks the full range of metric and imperial nut types across all common property classes and finishes — hex nuts, nyloc nuts, flange nuts, dome nuts, castle nuts, wing nuts, coupling nuts, weld nuts, and more. Available in zinc-plated, hot-dip galvanised, and stainless steel (304 and 316). Shop All Lock Nuts Nylon Lock Nuts Pair this guide with our Tap Drill Size Chart for the right pilot drill diameter at every tap size. For thread specs, grade markings and metric-to-imperial conversions, see our Fastener Reference Guide. For powder, granular, and bulk-material flow aid, see the AIMS industrial pneumatic vibrator range. For lang tools, see our lang tools range stocked across Australia.
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