Which best describes a copper fitting?

A copper fitting is best described by the characteristic of needing to be soldered at one end. This fitting is typically used in plumbing applications for connecting various pieces of copper tubing. The soldering process involves melting a filler metal into the joint to create a solid and leak-proof connection, which is essential for ensuring the integrity and longevity of plumbing systems.

Different types of copper fittings can vary in their specific characteristics, such as whether they have threads or how they can connect to other pipe fittings; however, soldering is a fundamental method employed for creating reliable joints in most copper piping systems. It is important to note that not all copper fittings are threaded at both ends, and many do not require a coupling at all, which differentiates this particular answer from the others that may suggest different attributes. Understanding the role of soldering emphasizes the importance of proper installation techniques in the plumbing trade.