Metric Din 6921 Class 8.8 Indent Hex Flanged Washer Serrated Screw Full Thread Zinc

Designed for use in applications where loosening forces, such as vibration, are present. After being installed, the serrations grip to the bearing surface so that significantly greater torque is needed to loosen the fastener than to tighten it. Can eliminate the need for a lockwasher or locknut in certain applications