Metric DIN 128 Type A and B Spring Lock Washers are specialty spring lock washers – Both are split metal rings that are bent into a curved (Type A) or waved configuration (Type B). Unlike standard split helical spring lock washers, the DIN 128 lock washers are non-directionally specific allowing the screw and or nut to be tightened in a clockwise or counter-clockwise manner. When compressed by tightening the nut, the DIN 128 lock washer exerts a spring force between the tightened bolt and the substrate creating frictional resistance to rotation.