Nylon Insert Lock Nuts Zinc (Stainless): Hex nut with a nylon-filled collar at its back end. When a screw reaches the collar, the threads and nylon form a tight, frictional fit, restricting movement of the screw when subjected to vibration. Designed to be used with like material machine screws and bolts. It is able to be reused. Nylon will begin to deteriorate at temperatures from 150-350 degrees F. Also available in stainless steel for applications which dictate the need for a corrosion resistant fastener...