The M4 x 18W8 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 metal together. It is made of steel and has a zinc-plated finish. The split washer helps to distribute the load of the screw or bolt, and the flat washer helps to prevent the screw or bolt from sinking into the material. The Phil Pan head has a rounded top and a slotted drive. This type of fastener is commonly used in automotive and industrial applications.