locknut

A locknut is a nut designed to resist loosening when subjected to vibration, shock, or dynamic loading. The locking action can be achieved by friction, deformation, or a combination of both, so that the nut remains in place relative to the bolt or stud.

Common types include nylon-insert locknuts, also known as nyloc nuts, which encase the threaded portion in a nylon sleeve that deforms to create friction as the nut is tightened. Prevailing-torque locknuts use a deliberately deformed or hardened thread surface that requires higher torque to rotate, providing a positive locking action without additional components. Jam nuts are standard nuts that are backed up by tightening a second nut against the first to lock it in place. Serrated flange locknuts include a toothed surface that bites into the mating part, increasing resistance to loosening. Other locking nuts rely on distorted or deformed threads to generate a locking force.

Locknuts are used in a wide range of applications, including automotive, aerospace, machinery, bicycles, and consumer electronics, wherever vibration or dynamic loads could loosen conventional nuts. They are typically made from steel, stainless steel, or brass, and include versions with nylon inserts, high-strength alloys, or steel with zinc or other coatings for corrosion resistance.

Installation and maintenance considerations include following manufacturer torque specifications, ensuring clean threads, and selecting the appropriate type for the service environment. Nylon-insert locknuts may have limited reusability under high temperatures or chemical exposure, while mechanical locking types are generally more durable but may retain debris. Alternatives to locknuts include thread-locking adhesives.