The M3 x 18W7 JIS B1188 Phil Pan Split Washer Flat Washer Sems M/S Zinc is a type of fastener that is used to secure two or more pieces of material together. It is made of steel and has a zinc coating for corrosion resistance. The washer has a split design that allows it to be easily installed and removed. The flat washer helps to distribute the load of the fastener and prevent it from damaging the material. The Sems M/S designation indicates that the fastener is self-locking, meaning that it will not loosen over time.