Product Description Hillman has the specific screws and bolts you need for your building projects. Carriage bolts are designed to fasten a wooden surface to either a wood or metal frame. The smooth, domed head screw offers a semi-flush, low-profile finish to applications. To install, simply drill a hole in the surface that matches the diameter of the fastener, insert the bolt, and connect the nut on the other end. No washer is needed because its square shoulder locks into the material as the nut is tightened. These round head fasteners will last for years thanks to their galvanized finish, which offers optimal protection against rust and corrosion. From the Manufacturer Carriage Bolts have a smooth, rounded head that has a small square section underneath. They are used in wood connections utilizing the square neck under the round head which will sit into the hole to prevent the head from turning. These carriage bolts come plated in zinc for moderate corrosion resistance.