Heavy Duty Stud Master : Spurtar 1/2 inch drive stud puller, broken bolt extractor, nut remover suitable for 1/4 inch to 3/4 inch ( 6mm to 19mm ) studs from engine blocks, exhaust manifolds, cylinder heads, and other applications Optimum Fit Stud Extractor: Knurled roller uses cam action to grasp the stud firmly and secures optimum fit while minimizing damage to threads. Cam rotates to grip onto the stud for quick and easy use. Help easy out bolt extractor set studs quickly and efficiently Safe Stud Extractor Tool: Spurtar professional tools are for commercial or occasional use. Suitable for safely removing broken or seized bolts and studs. 2 holes 1/2" (14mm) and 3/4" (19mm) allow for an optimal fit and minimize thread damage Bolt Extractor Operation Guidance: Use with 1/2-inch drive ratchet wrench or flex handle and turn the extractor to engage the cam and stud to tighten, then turn until the stud is removed. Rounded bolt Remover Unique design: The design allows the tool to be flush with the mounting surface of the stud, so it can grab a stud that breaks off very close to the mounting surface., Manufacturer: King Company