Technical article · 5 min read
Nut locking types compared: nylon insert, all-metal, flange and more
Vibration loosens joints. Here is how the common locking methods work — and where each one fits.
A bolted joint stays tight as long as the clamp load holds. Vibration, especially sideways movement of the joint, can make a nut turn back. Locking features either add friction (prevailing torque), stop the nut turning (positive locking) or bond the thread.
Prevailing-torque nuts
- Nylon-insert nuts (DIN 985 / ISO 10511, DIN 982 / ISO 7040) — a polyamide ring grips the bolt thread. Simple and reliable; limited by temperature (nylon softens well below steel limits) and best not reused many times.
- All-metal lock nuts (DIN 980 / ISO 7042) — the top of the nut is slightly deformed, so it grips the thread. Suits higher temperatures and painted or plated parts.
- Performance of both types is defined by ISO 2320.
Flange and serrated flange nuts
The integral flange spreads load; serrations under the flange bite into the joint surface and resist turning. Good for steel joints that are not painted or soft.
Positive locking
Castle (slotted) nuts with a cotter pin cannot turn at all once pinned. They are used where safety matters more than speed of assembly — steering and suspension joints, for example.
Pre-applied patches
A nylon patch (DIN 267-28) or a micro-encapsulated adhesive is applied to the thread at the factory. The part arrives ready to fit, with no loose washers or liquid adhesive on the line.
A note on spring washers
Split spring washers (DIN 127) are still widely used, but many vehicle and machine makers have moved to flange nuts, prevailing-torque nuts or patches for joints that see vibration. Follow the drawing — and ask if you are unsure which method suits your joint.
Standards and values are summarised for general guidance — always work to your drawing and the current edition of the standard. Related REL page.
