Removes Broken Exhaust Manifold Bolts on GM LS III 4.8L, 5.3L, and 6.0L Motors Without Damaging the Cylinder Head. Tapered bolts center base plate over bolt holes and slip fit bushing allows you to move from hole to hole without moving base plate. The screw extractor is then used to remove the broken bolt. Includes bushing to drill to tap size when extractor cannot be used. Double sided drill depth gauge to make sure water jacket is not pierced. 71450 LOCK SCREWS HOLD BUSHING IN PLACE Bushings are hardened steel with a Rockwell of 58-64 heat treat