The M5-0.8 x 20W10 JIS B1188 Phil Pan 304SS Split Washer 302/304SS Flat Washer Sems A2 Stainless is a type of fastener that is used to secure two or more pieces of material together. It is made of stainless steel, which makes it resistant to corrosion and rust. The washer has a split design, which allows it to be easily installed and removed. The flat washer helps to distribute the load of the screw or bolt, preventing it from damaging the material.