Fender washers are flat washers with a larger outer diameter in proportion to its center hole. Used where an extra wide bearing surface is required. Flat washers are used under bolt heads or nuts to increase the bearing surface area, or to offer protection so that the nut or bolt can be rotated without distortion of the bearing surface. Flat washers are also used to give tightness to a joint, to prevent leakage, and especially to distribute pressure under the head of a bolt or nut. Dimensional specifications are governed by ASME B18.21.1. Fender washers were originally designed for auto body repair work, they are also used in sheet metal, plumbing, and electrical work. Also used to attach signs to posts, to install drywall and wood paneling. Available in zinc plated finish. Zinc plating sacrifices itself, corroding before the base material, offering added corrosion resistance.