What is prevailing torque?

Prevailing torque is the amount of torque needed to screw a locking nut down a thread.

On most metal locknuts, the prevailing torque is created by distorting the top threads (double slotted) of the nut in some way.

so in a way you encounter resistance while driving the fastener down to the thread. 

the advantage of the Auto-Lok nut is that the deformation is vertical and does not damage the male threads, which makes the nut re-usable compared to a deformed axial nut

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