In order to assure the unique wedge locking function of the NORD-LOCK washers, the hardness of the mating surfaces should not exceed the hardness of the NORD-LOCK washers.

The unique wedge-locking action of the NORD-LOCK washers can easily be verified. Tighten the bolted joint with NORD-LOCK washers, then untighten. During untightening, sliding must always occur between the pair of NORD-LOCK washers. Upon overriding of the cam faces a "click effect" should be felt when the nut/bolt comes loose. Ocular inspection of the mating surfaces should show clear impression marks made by the NORD-LOCK washers. When all these criteria are fulfilled, NORD-LOCK washers will always safely lock bolted joints exposed to severe vibration or dynamic loads.