Big Twin tappet blocks do not have counterbored bolt holes; so, when a tappet block is removed (or even loosened) it should be reinstalled using an alignment tool to ensure that the lifters track properly on the camshaft. This 1/4-20 tapered shank is designed to provide perfect alignment when used to align the oil hole from the engine crankcase to the lifter/tappet guide block in (late) 1976-2017 Harley Big Twin Shovelhead, “EVO”/Evolution & Twin Cam Models. (Two tools are always recommended for the best alignment, but not required for this process) Can also be used to align the Rocker Box Bases on Evolution heads (TWO TOOLS REQUIRED FOR THIS PROCESS) Can also be used to align the Oil Pump to the Cam Support Plate on Twin Cam models. (TWO TOOLS REQUIRED FOR THIS PROCESS) Sold Individually Replaces HD Pt# 33443