The steel lag screw with hot-dipped galvanized finish as a hex head and meets American Society of Mechanical Engineers ASME B18.2.1 and American Society for Testing and Materials ASTM A307 specifications. Steel is often used in applications where strength is the primary consideration. The hot-dipped galvanized finish offers excellent corrosion resistance. The hex head has six flat sides that a wrench can grip to turn the screw from the side, enabling use when there is no space above the head for a driver.Lag screws, also called lag bolts, are hex-headed threaded fasteners commonly used for wood-fastening applications where load bearing is a factor. Usually longer than wood screws, lag screws are inserted into a drilled hole and secured with a nut.