Set of 2 Pieces Quality Tap Guides for True Tapping. Shank is 1/2" Straight/ Parallel Spring Center Tap Guide Tool to Align Tap for threading Lathe Mill Jig Bore AGTGK-128 Made of precise hardened alloy steel. Point hardened to 50-55 HRC 12 mm (1/2") shank with a spring loaded centre and 85 mm is overall length. AGTGK-127 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. DETAILS OF PRODUCT Ref: AGTGK-128 Made of precise hardened alloy steel. Point hardened to 50-55 HRC 12 mm (1/2") shank with a spring loaded centre and 85 mm is overall length. DETAILS OF PRODUCT Ref: AGTGK-127 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.