The Nord-Lock lock washers have wedge surfaces on one side with a cam angle greater than the pitch angle of the bolt thread. Radial ribs can be found on the opposite side. The washers are supplied in pairs with the wedge surfaces glued to one another. When the bolt and/or nut is tightened, the opposing wedge surfaces and the external radial ribs mechanically interlock with the surrounding material. Movement is only possible between the wedge surfaces. Any attempt from the bolt/nut to rotate loose, for example due to vibration, is blocked by the wedge effect creating increased pretension. The connection can be loosened manually once the increased pretension is overcome.