12-Piece Carbon Steel NPT Pipe Tap and Die Set in Case 1/8 in., 1/4 in., 3/8 in., 1/2 in., 3/4 in. and 1 in. in Wooden Case About the Taps: Also called Pipe Taps, National Pipe Taper Taps are appropriate for threading a wide variety of materials both ferrous and non-ferrous. Carbon steel pipe taps are designed to clean and or re-thread damaged or jammers pipe threads. 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 chamfer. NPT threads require the use of a sealer like Teflon tape or pipe compound. About the Dies: Drill America Hex Dies are for rethreading over bruised or rusty threads. They are the most cost effective type of rethreading tool available. No special holder is required for this type of die.