Drill America T/A64013 2" NPT HSS 7 Flute Pipe Tap, Tap America, T/A64013Drill America T A64013 2" NPT HSS 7 Flute Pipe Tap, Tap America, T A64013 National Pipe Taper Taps (NPT) are appropriate for threading a wide variety of materials both ferrous and non ferrous. The nominal size of a Pipe Tap is that of the pipe fitting to be tapped, not the actual size of the tap. The thread tapers 3 4 of an inch per foot. All Pipe Taps furnished with a 2 1 2 to 3 1 2 thread chamger. NPT threads require the use of a "sealer" like