3/8"-18 NPT HSS 4 Flute Pipe Tap NPT threads require the use of a "sealer" like teflon tape or pipe compound. All Pipe Taps furnished with a 2-1/2 to 3-1/2 thread chamger. The nominal size of a Pipe Tap is that of the pipe fitting to be tapped, not the actual size of the tap..
~ DIN6499B ~ The powerful clamping ability and durability are ideal for boring, milling, reaming, drilling and tapping as well as grinding operations in high precision machining.