A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,[1] stiff nut[1] or elastic stop nut,[2] 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.[2] Free-spinning locknuts exist which carry the advantage of not requiring extra torque until seated.[3]