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 (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.

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.

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.

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?

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.

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:

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.