Engineering Guide · 8 min read
DIN 985 vs DIN 980: Nylon-Insert and All-Metal Lock Nuts
Compare DIN 985 nylon-insert and DIN 980 all-metal lock nuts, their current ISO routes, temperature limits, tightening and reuse requirements.
The short answer: DIN 985 specifies a thin hex lock nut with a non-metallic insert, commonly supplied as nylon; DIN 980 specifies an all-metal prevailing-torque hex nut. Both DIN editions are withdrawn. For a new coarse-thread specification, compare ISO 10511:2025 for the thin insert-nut form with ISO 7042:2025 for the high all-metal form. Check load capacity and dimensions as well as the locking mechanism before approving a substitution. Both locking mechanisms resist rotation; the joint still needs its specified clamp load.[1][2][9][10][4][5][8]
This article is part of How to Specify a Bolt. It compares prevailing-torque hex nuts, whose locking feature works in the mating thread. For the wider choice of locking methods, see lock washers and other ways to resist loosening.
What creates the locking resistance?
A nylon-insert nut has a captive polymer ring that grips the mating thread as the bolt passes through it. An all-metal prevailing-torque nut uses a controlled interference in its metal locking section, often produced by deforming part of the threaded body. Both are friction-locking designs.[1]
You can feel that resistance before the nut reaches the joint. The torque needed to turn an engaged, unseated lock nut is called prevailing torque, or running torque. At that point, the nut is resisting rotation but has not begun to clamp the parts together.[7]
A nut can feel tight before the joint is tight. That distinction matters when replacing a plain hex nut: the locking feature changes the torque required during installation. Use a tightening instruction that covers the actual bolt, lock nut, finish and lubricant.
Nylon insert or all metal: compare the application
Start with the conditions at the nut, then compare the proposed parts. The table below is a selection checklist, not a ranking of vibration resistance.
| Selection question | Nylon-insert nut | All-metal nut |
|---|---|---|
| What creates the locking resistance? | A polymer insert provides the locking interference. | A metal locking section provides the interference.[1] |
| Is the joint hot? | Check the complete nut's rating, including its insert, body material, finish and lubricant. | Check the complete nut's rating, including its material, finish and lubricant. |
| Are fluids or cleaners present? | Check insert, metal and coating compatibility with the named chemicals. | Check corrosion and lubricant compatibility for the actual exposure. |
| Will it be dismantled? | Insert wear can reduce locking resistance. | The metal locking feature can also wear with use.[6] |
| Will it fit? | Check nut height, socket access and full insert engagement. | Check the particular locking form and its installation direction. |
For an indoor equipment bracket with moderate temperatures, a nylon-insert nut may meet the requirement once its size, strength and installation method are confirmed. For a bracket beside a hot duct, obtain the maximum temperature at the fastener and compare it with the proposed nut's rating. Where transverse movement is the main problem, assess the joint's clamp load and movement as well as the locking device.[1]
What do the temperature numbers mean?
ISO 2320:2015 distinguishes laboratory test temperature from the application ranges described in its scope. These numbers apply to the steel prevailing-torque nuts covered by that standard.[2]
| ISO 2320:2015 condition | Temperature | How to use it |
|---|---|---|
| Functional-property testing | +10 to +35 °C | Ambient range for the combined prevailing-torque and torque/clamp-force test. |
| Non-metallic insert nuts | −50 to +120 °C | Application range noted in the scope; check the proposed insert and product rating. |
| All-metal nuts | −50 to +150 °C | Application range noted in the scope; hotter service needs a specifically rated product. |
Select a part whose published rating covers the stated service conditions. For example, Bossard lists an operating limit of 70 °C for its BN 33024 A2 stainless steel nut with a polyamide insert and specified coating. That is a limit for the complete product, lower than the scope's +120 °C figure.[8] State the expected continuous temperature, peaks and exposure duration when requesting confirmation.
The standard also warns that temperature outside the test range can change locking and torque/clamp-force behavior. For elevated-temperature service, request performance data for the proposed assembly at the required temperature.[2]
Specify the nut form as well as the locking type
DIN 985:1987-05 covers the thin nut with a non-metallic insert. DIN Media identifies DIN EN ISO 10511 as its replacement route. DIN 980:1987-05 covers the all-metal form; its replacement record names separate DIN EN ISO 7042 and DIN EN ISO 10513 routes for coarse and fine threads.[9][10]
When a drawing calls for DIN 985 or DIN 980, keep that requirement until the drawing owner approves the proposed replacement. Compare the full dimensions, wrench access, thread pitch and mechanical requirements. The ISO product-form and size ranges below help identify which current coarse-thread standard to check.
“M10 lock nut” leaves the body height and load capacity unresolved. These current coarse-pitch product standards distinguish regular, thin and high nuts:
| Product standard | Nut form | Coarse-thread range |
|---|---|---|
| ISO 7040:2025 | Regular hex nut with non-metallic insert | M3–M39[3] |
| ISO 10511:2025 | Thin hex nut with non-metallic insert | M3–M39[4] |
| ISO 7042:2025 | High hex nut, all metal | M5–M39[5] |
The table summarizes published scopes, not dimensions or interchangeability. The two insert-nut standards address sizes below M5 separately in Annex A. Their scopes cover non-metallic inserts; specify nylon if that particular insert material is required.[3][4]
ISO 10511:2025 explicitly warns that thin nuts have reduced loadability compared with regular or high nuts. A shorter nut can solve a clearance problem while changing the connection's load capacity. Confirm the required nut property class and bolt pairing before approving the change.[4] For existing plain-nut drawings, the DIN 934 and ISO 4032 comparison explains why thread fit alone is insufficient.
How should tightening torque account for the lock?
Measure running torque while the locking feature is fully engaged and the nut is still clear of the bearing surface. After seating, the applied torque must also overcome bearing friction and develop bolt tension. L3Harris's P-553 Rev. 03 makes this distinction in its assembly procedure.[7]
Follow the drawing or equipment manufacturer's instruction for whether running torque is included in the stated setting. L3Harris permits an addition when engineering instructions specify it and warns against making that adjustment independently. Its procedure governs its own products; it illustrates why a generic instruction to “add the lock-nut torque” is incomplete.[7]
Ask for the required final setting and tolerance, the lubrication condition and the method for checking clamp load where required. Keep those conditions with the assembly instruction. The bolt torque guide explains what must accompany a usable torque value.
Can either type be reused?
Both types can lose locking resistance as their locking features wear. PennEngineering identifies this limitation for nylon-insert and collapsed-thread designs.[6] Reuse therefore needs a defined rule for the particular nut and application.
ISO 2320:2015 clause 8 sets a maximum prevailing-on torque at the first installation and minimum prevailing-off torque at the first and fifth removals. These are limits on the locking resistance, distinct from the final tightening torque used to clamp the joint. The controlled test cycles do not authorize five service reuses after heat, corrosion or damage.[2]
Follow the equipment's replacement instruction first. If reuse is permitted, apply its inspection and running-torque requirements to the specified hardware combination. Replace a nut with damaged threads, a damaged insert or locking resistance outside the permitted limits.
What to put on the RFQ
State the exact nut form on the RFQ. This example specifies a regular-height steel nut with a nylon insert to ISO 7040; it is a different form from the thin DIN 985 / ISO 10511 nut. Use the thin-nut standard only after confirming that its reduced loadability meets the connection requirement.[3][4]
| Field | Example inquiry |
|---|---|
| Product | Regular hex lock nut with nylon insert |
| Product standard | ISO 7040:2025 |
| Thread | M10 × 1.5 |
| Material and strength | Steel, nut property class 8; confirm suitability for the specified class 8.8 bolt |
| Finish | Plain, uncoated; identify any supplied lubricant |
| Operating conditions | Indoor bracket, +5 to +60 °C; no process-fluid contact |
| Assembly and maintenance | New nut at each reassembly; provide the applicable tightening instructions |
| Documents and quantity | Confirm insert material, temperature rating and locking-test requirements; 1,000 pieces |
The temperatures above are example application requirements, not measured results or a product rating. For an all-metal alternative, request a separate quotation naming its standard, nut form, material, strength and finish, then review it against the same service conditions.
Send the drawing and operating conditions to request a quote for the specified nut and mating hardware.
References
- Bolt Science. Self-Loosening of Bolts and Nuts. Friction-locking mechanisms, joint movement and the first/fifth removal checks discussed in its prevailing-torque section.
- ISO. ISO 2320:2015 — Fasteners — Prevailing torque steel nuts — Functional properties. Current edition confirmed in 2025; scope, laboratory test conditions, temperature notes and clause 8 locking-torque limits. National standards body preview.
- ISO. ISO 7040:2025 — Regular nuts with non-metallic insert. Product form, coarse-thread range and treatment of sizes below M5.
- ISO. ISO 10511:2025 — Thin nuts with non-metallic insert. Product scope and reduced-loadability warning.
- ISO. ISO 7042:2025 — High nuts, all metal. Product form and M5–M39 coarse-thread scope.
- PennEngineering. Locking Nuts. Nylon-insert and collapsed-thread locking features and wear during repeated use.
- L3Harris. P-553, Rev. 03 — Torque Application Procedure, effective April 16, 2026. Definitions and §4.2.2 on running torque and authorized torque adjustments; an OEM procedure, not a universal installation standard.
- Bossard. BN 33024 — Thin prevailing-torque hex lock nuts with polyamide insert. Published product-specific operating temperature of up to 70 °C.
- DIN Media. DIN 985:1987-05 — Prevailing torque type hexagon thin nuts with nonmetallic insert. Withdrawn edition and its DIN EN ISO 10511 replacement record.
- DIN Media. DIN 980:1987-05 — All-metal prevailing torque type hexagon nuts. Withdrawn edition and the separate DIN EN ISO 7042 / DIN EN ISO 10513 replacement routes.