Cobalt alloy bit provides maximum cutting force to open bolt faces to magnum dimensions. Back rake, front and side clearance, lip angle, cutting angle and chip rake are ground to give best performance in bolt steels. A must if you don't have a tool-post grinder. Mfg: Brownells SPECS: 21⁄8" (5.4cm) long. 1⁄4" (6.3mm) or 5⁄16" (7.9mm) square.