Union Butterfield 1568(NPT) High-Speed Steel Pipe Tap, Interrupted Thread, Uncoated (Bright) Finish, Round Shank With Square End, 3/8"-18 Thread Size Pipe tap cuts threads in pipes and pipe fittings NPT (National Pipe Taper) threads for tapered pipe threading Straight flutes to cut threads in through holes and blind holes Interrupted thread for greater flow of lubrication and better chip disposal than continuous thread Round shank with square end helps to minimize rotation in the tool holder