Spring Center Tap Guide Tool to Align Tap for threading Lathe Mill Jig Bore A Very Handy DIY tool for Perfect Tapping Made of precise hardened alloy steel. Point hardened to 50-55 HRC 1/2" diameter hardened shank, knurled for easy handling Adjustable Tension Spring 3/16" Hardened tension pin For execution, the center's body should be gripped in a drill chuck or collet, while the hardened point is inserted into the middle of the tapping handle. The stroke of the center will follow the tap, assuring straight and accurate hand tapped threads. One universal size for all tapping applications.