The M3-0.5 x 16W6 JIS B1188 Phil Pan 304SS Split Washer 302/304SS Flat Washer Sems A2 Stainless is a type of fastener used to secure two or more pieces of material together. It is made of 304 stainless steel, which is resistant to corrosion and rust. The split washer helps to distribute the load of the fastener, while the flat washer helps to prevent the fastener from sinking into the material. The Sems A2 stainless steel finish provides additional corrosion resistance.