Spline sockets also known as triple square or XZN sockets feature twelve splines or points arranged in a double hexagonal shape designed to loosen or tighten fasteners with a 12-point spline head. Spline sockets have internal splines and fit over the top of a fastener to tighten or loosen it. Spline bit sockets terminate with a 12-point spline bit which is designed to fit into the corresponding spline shaped recess in spline head in the fastener. Spline sockets are often used in the automotive industry where spline fasteners are found in components such as wheel hubs and drive shafts.