DIN 128 single coil spring lock washers.
Metric DIN 128 Spring Lock Washers are specialty spring lock washers – Both are split metal rings that are bent into a curved or waved configuration.
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 exert a spring force between the tightened bolt and the substrate creating frictional resistance to rotation.