Fastener Guide / Technical Reference

Prevailing-Torque All-Metal Locknuts

All-metal locknuts use a distorted or deflected thread to grip the bolt. They work above nylon temperature limits.

Last reviewed 2026-09-10 · Governing standard: IFI 100/107; ISO 7042 · reference FG-4A5CC9 · Report an error on this sheet

Before you use a torque value: these are starting estimates for general bolting. Do not use them for pretensioned or slip-critical structural joints (ASTM F3125 A325/A490 under RCSC) — those are installed by turn-of-nut, calibrated wrench, twist-off or DTI methods. Lubrication changes the answer: a dry value applied to a lubricated or plated bolt can yield or break it. The manufacturer’s or engineer’s value always governs.

Common styles

StyleHow it grips
Top-lock (Stover type)Top threads crimped oval
Two-way reversibleCenter-deflected threads
Flex / beam topSlotted top segments pinched inward

These tables carry the same figures as the printed sheet below.

The printed sheet

Prevailing-Torque All-Metal Locknuts

See an error on this sheet?

Tell us what is wrong.

Text version of this sheet

All-metal prevailing-torque locknuts · ISO 7042

FIELD IDENTIFICATION

What it is

All-metal locknuts use a distorted or deflected thread to grip the bolt. They work above nylon

temperature limits.

All-metal locknut: deformed top threads (crimp

dimples shown)

Common styles

Style

How it grips

Top-lock (Stover type)

Top threads crimped oval

Two-way reversible

Center-deflected threads

Flex / beam top

Slotted top segments pinched inward

Key points

Harder on bolt threads and less reusable than nylon.

Governing standards: IFI 100/107; ISO 7042. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take precedence over

this sheet.

torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability

arising from reliance on this reference.

Fastener Guide reference FG-4A5CC9 · thefastenerapp.com/fastener-guide/technical-reference/prevailing-torque-all-metal-locknuts · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.

Related sheets

← Nylon-Insert LocknutsZinc-Plated Fasteners →

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