the steel lag screw with plain finish has a hex head & meets american society of mechanical engineers asme b18.2.1 & american society for testing & materials astm a307 specifications. Steel is often used in applications where strength is the primary consideration. 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 & secured with a nut.