Serrated face nut
Encyclopedia
A serrated face nut is a locknut
with ridges on the face of the nut
that bite into the surface it is tightened against. The serrations are angled such that they keep the nut from rotating in the direction that would loosen the nut. Because of the serrations they cannot be used with a washer or on surfaces that cannot be scratched. Sometimes both faces of the nut are serrated, permitting either side to lock.
Locknut
A locknut, also known as a lock nut, locking nut, prevailing torque nut, stiff nut or elastic stop nut, is a nut that resists loosening under vibrations and torque. Elastic stop nuts and prevailing torque nuts are of the particular type where some portion of the nut deforms elastically to provide a...
with ridges on the face of the nut
Nut (hardware)
A nut is a type of hardware fastener with a threaded hole. Nuts are 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...
that bite into the surface it is tightened against. The serrations are angled such that they keep the nut from rotating in the direction that would loosen the nut. Because of the serrations they cannot be used with a washer or on surfaces that cannot be scratched. Sometimes both faces of the nut are serrated, permitting either side to lock.