When conductivity in mounting surfaces is an issue for fasteners, use nylon shoulder washers. The purpose of a shoulder washer is to insulate the metal fastener (screw or rivet) or wire from the rest of the fabrication or assembly. Also, for rotary applications, shoulder washers can be inserted into a housing to provide a bearing surface. The flange on the shoulder washer provides a couple of functions: it can positively locate the bushing when installed, or it can provide a thrust bearing surface. Shoulder washers may vary by barrel length, the screw or bolt size they for which they are intended, shoulder outside diameter, shoulder length, flange outside diameter, and the amount of washers in a package, among other considerations. For more on washers, see our flat washers, retaining ring washers, lock washers, or sealing and cushioning washers.