Nylon insert locknuts are hex nuts with a nylon-filled collar. When a screw reaches the collar, the threads and nylon form a tight, frictional fit restricting movement of the screw when it is subjected to vibration. Designed to be used with like-material machine screws and bolts, nylon insert locknuts can be reused more times than a two-way reversible nut, however, nylon will begin to deteriorate at temperatures of 150°-350°F so they are not recommended for high temperature service. Typical hardness will reach a maximum of Rockwell C28. Nuts are manufactured to meet a proof load of 90,000 psi minimum.