What is prevailing torque?

Please help? What is prevailing torque? Im lost!

This term is typically used for locking type fasteners. It means that some torque is required always, to turn the nut or screw. If you have a simple hex nut on a screw, the "prevailing" torque is zero when the nut no longer contacts the surface and therefore is loose and can come off. If you use a prvailing torque type of nut(interference threads, plug of nylon in the threads or top), even if the nut backs off, some torque is required to further loosen it so it is less likly to fall off.

Hi Craig

Thanks for your reply so it would be best described as :

Torque required to continue to loosen a fastener once the initial break occurs?

Thanks

Irish