Prevailing Torque

Prevailing torque is the built-in resistance to turning found in certain “locking” fasteners, created intentionally so the fastener resists loosening under vibration. It is the torque required to rotate the nut or screw on the threads before the joint surfaces are clamped (and likewise the torque required to keep it turning during removal). This resistance comes from a locking feature that adds friction or interference in the threads, rather than from clamp load.

Prevailing torque is commonly associated with prevailing-torque locknuts (like all-metal distorted-thread nuts), nylon-insert locknuts, and thread-patch or pellet-coated screws. Specifications often set acceptable prevailing torque ranges to ensure the fastener locks reliably without making installation impractical or causing thread damage. Because prevailing torque can change with lubrication, coatings, installation speed, temperature, and reuse, it’s important to follow the specified fastener type and installation conditions to maintain consistent locking performance.