The M4 x 30W9 JIS B1188 Phil Pan Split Washer Flat Washer Sems M/S Zinc Yellow is a type of washer that is used to distribute the load of a screw or bolt over a larger surface area. It is made of a zinc-plated steel and has a split design that allows it to conform to the shape of the surface it is being used on. The washer has a diameter of 4mm and a thickness of 0.9mm. It is designed to be used with screws or bolts that have a diameter of 4mm. The washer is yellow in color and has a smooth finish.