Washer, lock, serrated, internal, zinc plated, GR 4.8, M24, 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. Zinc plated fasteners are the most common used plating. This ensures good rust-resisting qualities, appearance and low cost.