Washer, lock, serrated, internal, stainless steel, GR A2-304, M3, Fastbolt.

Serrated lock washers increase the friction between the bolt head/nut and the mating surface. They do this by gripping into the mating surfaces. Serrated lock washers are installed between the bolt head/nut and the mating surface. The bolted joint is then tightened in the same way as an unsecured bolt. Internal tooth lock washers have teeth around the center hole. Stainless steel is a family of iron-based alloys that contain a minimum of approximately 11% chromium, a composition that prevents the iron from rusting, as well as providing heat-resistant properties.