The Summit Racing Bust-N-Out Bolt Removal Tool Kits are designed for use with a high-speed die grinder. The kits come with two end cut carbide burrs to prepare broken fasteners for final drilling through their centers with the included drill bit. This helps increase the ability to drill the broken bolt on-center. That helps save the existing threaded hole and component. The kits are available for the following fastener sizes: 1/4" and 6mm, 5/16" and 8mm, 3/8" and 10mm, 7/16" and 12mm, and 1/2" and 14mm.