The nominal diameter is the diameter of the external screw used, and the inner diameter of the washer has a slightly larger hole.
Stainless steel (SUS304) for excellent corrosion and heat resistance.
It is used to distribute the surface pressure when fastening with bolts, small screws, nuts, etc., and to prevent damage to the mating member, and to prevent caving when the bottom hole is large.
As it has excellent corrosion resistance, it can be used in places with high humidity or objects outside.