Union Butterfield 1580(UNC) High-Speed Steel Thread Forming Flute Tap, Uncoated (Bright) Finish, Round Shank With Square End, Plug Chamfer, H6 Tolerance, 1/4"-20 Thread Size Cold-forms threads in through holes and blind holes without producing chips Spiral forming lobe pattern for reducing tapping torque High-speed steel for compatibility with a variety of materials Available in UNC (Unified Coarse) or UNF (Unified Fine) right-hand thread options for different applications Round shank with square end helps to minimize rotation in the tool holder