It is a type of fastener with a threaded hole and is almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads’ friction, a slight stretch of the bolt, and compression of the parts. In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed: Adhesives, safety pins or lock wire, nylon inserts, or slightly oval-shaped threads.