Washers are thin plates with a hole that is normally used to distribute the load of a fastener, such as a bolt, nut or rivet. Other uses are as a spacer, spring, wear pad, locking device, electrical insulator or to reduce vibration (rubber washer). Washers are selected by the inside and outside diameters, thickness, plating and material. Types include flat, external tooth, internal tooth, sealing or split lock.