Nuts screw onto male-threaded fasteners using matching female threads and tighten towards a mounting surface. Hex nuts have six sides and are the most common type of nut. Lock nuts resist rotation by locking into place. Cap nuts screw onto the ends of male fasteners to protect the threads from damage. Handle nuts, thumb nuts, and wing nuts are hand-driven nuts. Flange nuts resist marring the mounting surface as they are fastened into place. Coupling nuts connect two male fasteners. Cage nuts and spring nuts install into metal sheets or racks. Square nuts install into square-shaped openings, channels, or slots. Weld nuts are welded into place to provide a female-threaded mounting point. T-Nuts for wood embed into wood to provide a female-threaded mounting point.