For corrosion resistance you can't beat the glass reinforced products from Aickinstrut. This is a glass reinforced polyurethane hex bolt with molded flange collar. No need for a washer. See specs below. Part: 500PU-200 1/2" x 2" Hex Flange Bolt , Thread Shear: 450 lbs, Shank Shear: 870 lbs, Shoulder Length: 3/4", Torque: 8 ft/lbs, Includes: Pack of 25 Bolts.