These Cam Checking Tools slide down into the lifter bore and ride on top of the camshaft in order to measure lobe lift and base circle run-out. Comes complete with two followers: one for flat tappet or hydraulic cams and one for roller cams. Two different versions are available and each one is double ended. An O-ring on each end holds the tool securely in the lifter bore. For use with any standard dial indicator (not included).