Washers and Bushings with a shoulder are a disc or round shaped object with two levels, the smaller of the two diameters is usually inserted into an opening. The characteristics are thread/screw/hole size, diameter/inside, diameter/outside, diameter/shoulder, thickness/overall, length/below head, and material. The materials are brass, fiber, nylon, polyphenylene sulfide, polyphenylene sulfide/glass filled, and thermoplastic.