Drill America DWT64232 2"-11-1/2 NPT HSS Interrupted Thread Pipe Tap, DWT64232Drill America DWT64232 2" 11 1 2 NPT HSS Interrupted Thread Pipe Tap, DWT64232 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