Stanley Proto J1118SPL Box Spline Wrench 1/4-5/16" Spline fasteners help tighten high strength bolts which are used in high torque load applications. Spline helps reduce foreign object debris (FOD) by having a precise fit between the fastening tool and its fastener. Meets dimensional and open end performance requirements of ASME B107.100. Full polish finish provides corrosion resistance and an easy to clean surface. Meets Military Spec MS33787 for box end spline profile.