Union Butterfield 1545(NPT) High-Speed Steel Pipe Tap, High-Hook, Uncoated (Bright) Finish, Round Shank With Square End, 1/4"-18 Thread Size Pipe tap cuts threads in pipes and pipe fittings NPT (National Pipe Taper) thread design for tapered pipe threading Straight flutes to cut threads in through holes and blind holes High hook and deep flutes to manage long curly chips Round shank with square end helps to minimize rotation in the tool holder