This innovation tool actually slides down into the lifter bore and rides on top of the Camshaft in order to measure lobe lift and base circle runout. Each tool includes two followers: one for Solid or hydraulic cams and one for Rollers. Two models are available and each is double ended. Built-in o-ring Oldsmobile tool firmly in the lifter bore while 1" travel dial indicator (not included) reads Cam lift to .001" Two models available one for GM (.842" dia.) and Ford (.875" dia.) and another for Chrysler (.904" dia.) and Top Fuel (1.0" dia.) lifter bores.