This steel, zinc-plated hex nut has 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 it is subjected to vibration. While it is able to be reused more times than a two-way reversible nut, the nylon will begin to deteriorate at temperatures from 150-350 degrees (F). For use with bolts with a minimum tensile strength of at least 90,000 PSI. NLN38C