Mother Nature can be tough on your projects. DeckPlus is tougher. Carriage bolts are designed to fasten a wooden face to either a wood or metal frame. The low-profile domed head is designed to eliminate the need for a washer and provides a semi-flush finish to applications. The square underside of the head is self-locking to eliminate spinning and the need for a driving tool. DeckPlus exterior carriage bolts are finished with a Duplex coating that is 2x more corrosion resistant than galvanized fasteners. The coating offers 4 layers of protection from sun, temperature, rain, snow, sap, and chemicals found in treated lumber. The 4 layers are: zinc, chemical adhesion, two-epoxy coating, and durable protective finish. DeckPlus exterior carriage bolts are recommended for use with pressure treated lumber.