The proper name of the tool used to cut the threads of a steel pipe is called a:

The correct answer is that the tool used to cut threads on a steel pipe is called a die. A die is specifically designed for this purpose, as it cuts external threads into the surface of a pipe or rod. This threading is essential for connecting pipes and ensuring a secure fit in HVAC systems, plumbing, and various mechanical applications.

In contrast, a reamer is a tool used to enlarge or finish the inside of a pre-existing hole, ensuring a smooth or precise inner diameter but does not create external threads. A chuck generally refers to a clamping device used to hold an object in place, particularly in drill presses and lathes, and is not related to threading. A tap, on the other hand, is used to create internal threads within a hole but does not apply to cutting threads on the outside of a pipe. Understanding these definitions helps clarify why a die is specifically the appropriate tool for creating external threads on steel pipes.