With O-rings on each end to assure securing positioning, this unit slides down into the lifter bore and sits atop the camshaft for accurate measurement of lobe lift and base circle runout. Supplied with two followers, one for flat tappet or hydraulic cams, and the other for roller cams. Designed for GM (.842" dia.) and Ford (.875" dia.) applications. Includes 0-1.000" Dial Indicator 66962 (0.001")!