THESE WASHER HAVE CAMS OR WEDGES ON ON ONE SIDE , WITH A LEAD ANGLE GREATER THAN A THREAD ANGLE, AND RADIAL TEETH OR RIBS ON THE OTHER SIDE. THE WASHER ARE INSTALLED CAM FACE TO CAM FACE. WHEN TIGHTENING THE FASTENER TO PRELOAD, THE TEETH PENETRATE AND SEAT AGIANST THE JOINT MATERIAL AND NUT AND OR FASTENER HEAD. WHEN SUBJECT TO VIBRATION THE INTERACTING CAMS CREATE A WEDGE ACTION WHICH PREVENTS THE FASTENER FROM VIBRATING LOOSE.THESE ARE IDEAL FOR HIGH HEAT /HIGH VIBRATION AREAS.ZINC PLATED MADE IN SWEDEN.