What is the primary use of a ratchet stock in plumbing?

The primary use of a ratchet stock in plumbing is for threading pipes. A ratchet stock is a specialized tool that allows plumbers to create threads on the ends of metal pipes so that they can be joined together using threaded fittings. It engages the pipe and, using a die, cuts threads into the surface as it revolves around the pipe. This threading is crucial for ensuring that the pipes can properly connect, allowing for secure and leak-free joints.

The context of the other options can be understood through their specific functions: cutting pipes is done using pipe cutters, joining pipes typically involves techniques and fittings rather than threading, and repairing leaks often requires sealants or other methods depending on the type of material involved but does not utilize a ratchet stock. Thus, the correct identification of the ratchet stock's use is specifically tied to its role in the threading process, which is essential for effective plumbing work.