COMP Cams Tools 4915 COMP Cams Cam Checking Fixture was designed to maintain proper geometry while holding a dial indicator with extension right over the lifters. The professional quality tool is much easier to use and more precise than using a magnetic indicator base when degreeing a cam. This fixture is for use with the cylinder heads off the engine. Dial Indicator Fixture for Engine Block Attachment - 1/2" Head Studs COMP Cams Cam Checking Fixture for Use with Heads Off of Engine, 1/2" Head Studs Camshft Checker Tool