A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,[1] stiff nut, or elastic stop nut, is a nut that resists loosening under vibrations and torque. Prevailing torque nuts have some portion of the nut that deforms elastically to provide a locking action.Free-spinning locknuts exist, which do not require extra torque until seated.