PROTO® 1/2 inch drive deep sockets, spline. Proto® spline tools are designed to service high tensile strength fasteners used widely on military and commercial aircraft and in heavy machinery applications where vibration is prevalent. They are also used in automotive and industrial areas where high performance torque needs to be achieved. Spline sockets help tighten high strength bolts to high torque loads. They help lower the force required to turn standard fasteners by allowing the torque load to be moved away from the corners to help prevent fastener rounding. They also turn fasteners with damaged corners. Spline sockets on spline fasteners help deliver twice the torque of 12 point wrenches on double box fasteners and more torque than hex wrenches on hex fasteners. Spline helps reduce foreign object debris (FOD) by having a precise fit between the fastening tool and its fastener.