Back Home / Fasteners / Washers / FLAT WASHER USS ZINC 5/16″ THRU HARDENED FLAT WASHER USS ZINC 5/16″ THRU HARDENED SKU: 8FW56 Categories: Fasteners, Washers Used to improve stress distribution, and to span large holes. USS PATTERN. Made from heat treated thru-hardened steel, zinc yellow. Outside Diameter: 7/8″ Inside Diameter: 3/8″ Case Quantity: 100 Log In For Pricing