L.H. Dottie FWS516 5/16'' Stainless Steel Flat Washer. Stainless Steel Flat Washers are used to increase the surface area of fasteners, in order to evenly distribute the force applied when tightening them to a surface. They are also used to prevent loosening due to vibration, to stop the bolt or screw from pulling through, and act as spacers. They are manufactured from 18-8 stainless steel and are covered by the ASME B18.21.1 standard.