Nylock Nut, Nylon Insert Lock Nut

A nylon insert lock nut, also referred to as a nyloc nut, polymer-insert lock nut, or nylon insert (elastic) stop nut, is a common type of locknut comprised of a hex nut with a fixed nylon-filled collar at its back end. When a screw reaches the collar, the threads and nylon form a tight, frictional fit, thus restricting movement of the screw when it is subject to vibration. Nyloc nuts are designed to be used with machine screws and bolts and can be reused.