This tool is used to replace worn tappet rollers. The tool sets in a common bench vise. For '36-'83 and Evo tappets. Drill off ends with No. 7 drill (included) then drive out with 3/16" common pinch - clean up tappet body - install new roller and pin - then it crimps ends of pins in the center. Neato. We've done hundreds of tappets with this tool. The rollers pictured are "very early knuckle" before they used bearings . . . just a pin and solid spacer rollers.