Lock nut

A lock nut is a nut designed to resist loosening under vibration, shock, or dynamic loads. Standard hex nuts can gradually unscrew when subjected to repeated movement; lock nuts use various mechanisms to prevent this.

Common types

• Nyloc (nylon insert) nut: Has a nylon ring pressed into the top of the nut. As the bolt threads through the nylon, the material deforms and grips the threads, creating friction that resists rotation. The nylon can withstand temperatures up to about 120°C before softening.
• Prevailing torque nut: Deformed at the top so that the first few threads are slightly out of round. The bolt must be forced through this section, creating a mechanical interference that prevents loosening.
• Castle (castellated) nut: Has slots cut into the top for a cotter pin to pass through, physically locking the nut in position. Used on automotive ball joints and steering linkages.
• Jam nut: A thin nut tightened against a standard nut, creating a friction lock between the two. Common in plumbing and exhaust systems.
• Keps nut: A standard hex nut with an integrated free-spinning lock washer, combining two components into one for faster assembly.

When to use them

Lock nuts are essential wherever vibration is present: automotive suspensions, engine components, machinery, HVAC equipment, and any assembly subject to repeated loading. In critical structural applications, lock nuts supplement but do not take the place of proper torque procedures.