A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut or elastic stop nut, is a nut that resists loosening under vibrations and torque.

What does a locking nut do?

Lock nuts with nylon inserts (self‑locking nut, locking nut) are a prevailing torque, locking nut that resists loosening caused by vibration and normal use. Unlike free spinning nuts, lock nuts make use of a deforming elastic or metal material to stay in position against torque and shock.

When should you use a locking nut?

Locking nuts should be used when the screw joint consists of one or more soft materials. It is difficult to achieve and to maintain a high level of clamp load because the soft material deforms due to high surface pressure. This plastic deformation continues after the torque value has been applied to the screw.