A one-piece, self-locking nut is formed with a threaded nut body integrally formed with crush-locking lips on a forward contact face of the nut body spaced by an internal relief cut for accommodating deformation of the crush-locking lips therein. When the nut is tightened down on an object on a fastener bolt, the crush-locking lips are forced inwardly and deformed on the threaded shaft of the fastener bolt into the space of the internal relief cut in order to form a permanent lock on the fastener bolt. The one-piece, self-locking nut can be fabricated by conventional nut manufacturing methods. In use it threads on quickly like a conventional nut and installs with conventional tools.