The M4 x 16W8 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 is made of steel and has a zinc yellow finish. The washer has a split design that allows it to conform to the shape of the materials being fastened. The pan head design provides a large bearing surface that helps to distribute the load evenly. The washer is also self-locking, which means that it will not loosen over time.