Union Butterfield 1592(NPSF) High-Speed Steel Pipe Tap, Uncoated (Bright) Finish, Round Shank With Square End, 3/8"-18 Thread Size Pipe tap cuts threads in pipes and pipe fittings NPSF (National Pipe Straight Fuel) thread for leak-free straight pipe threading without the use of sealants Straight flutes to cut threads in through holes and blind holes Plug chamfer for correct perpendicular alignment, easier starting, and increased tap life Round shank with square end helps to minimize rotation in the tool holder