What is the primary purpose of a pipe nipple?

The primary purpose of a pipe nipple is to add length between fittings. A pipe nipple is essentially a short piece of pipe with threads at both ends, allowing it to connect two other threaded pipes or fittings and effectively extend the length of the piping system. This function is crucial in plumbing and other piping applications, where precise lengths are often needed to connect various components seamlessly. By using a pipe nipple, one can achieve the desired spacing between pipes or fittings without using additional components that might complicate the installation.

The other options, while they describe functions related to piping or fittings, do not accurately reflect the primary function of a pipe nipple. For instance, closing a pipe typically involves a different type of fitting, such as a cap, and reducing connections are made using specific reducing fittings rather than a nipple. Similarly, a stop for drainage would be more easily achieved with a valve rather than a pipe nipple. Thus, the correct identification of a pipe nipple's role emphasizes its convenience and utility in extending pipe length to create the necessary connections in a system.