In a pipe threading machine with NPT dies, what type of threads are designed to be cut?

The correct answer is National pipe threads, as NPT stands for National Pipe Tapered threads. This specific type of thread is designed primarily for use in piping systems to ensure a tight seal when connecting pipes. The NPT thread design features a tapered profile that allows for the threads to fit snugly over a range of diameters, which facilitates a secure and leak-free joint when pipes are threaded together.

In contrast, machine bolt threads refer to straight threads used primarily for fastening and securing machine parts, which differ significantly from the tapered design required for piping connections. New pipe threads is not a recognized standard in the context of threading, as the term does not refer to a specific design or standard used within the industry. Therefore, the best and most accurate choice that aligns with the functionality of a pipe threading machine is National pipe threads.