The M3 x 18W7 JIS B1188 Phil Pan Split Washer Flat Washer Sems M/S Zinc Yellow is a type of fastener that is used to secure two or more pieces of material together. It consists of a split washer, a flat washer, and a screw. The split washer is placed under the screw head, and the flat washer is placed over the screw head. The screw is then tightened, which causes the split washer to expand and grip the material. The flat washer helps to distribute the load of the screw, and the zinc yellow coating provides corrosion resistance.