Used on tow tractor, aircraft; assembly, cab; special aircraft and engine tool and support equipment parts; mrap buffalo mk2a2. 0.495" hole diameter 7/16 inch, flat washers, thru-hardened high strength, uss, yellow zinc plated core hardness: hrc 38 to 45; dimensions: asme B18.22.1, type a, uss plain washers zinc surface treated