Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of prevailing torque. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
A prevailing-torque fastener — nylon insert nut, deformed thread nut, or patch-lock bolt — resists rotation from first engagement. The torque needed to turn it is higher than the torque to keep it turning, and that difference is what resists vibration loosening.
It is one of the few locking methods that actually works. Split lock washers do not: testing shows they provide very little resistance and can reduce clamp load by flattening.
Common misuse
Relying on a split lock washer for vibration resistance. Use a prevailing-torque nut, a threadlocker, or correct preload instead.