Lag bolts are used to fasten wood to wood and metal to wood, attach objects to wood, and affix items to concrete and masonry when combined with lag expansion shields. They are heavy-duty wood screws that are available in larger sizes—both in terms of diameter and length—and usually have a hex head to facilitate higher installation torque using a wrench. While lateral strength is lower than a comparable bolt and nut, lag bolts are useful when access to one side of the joint is limited, the appearance of a nut is undesirable or through-bolt length is excessive. Lag bolts are also known as: hex lag bolts, lag screws, coach screws. Being a thread-forming-type screw, they create their own mating threads during installation—no nut is needed so a through-hole is not required.