Which of the following types of joints are not used to join copper tubing?

Flanged joints are indeed not commonly used for joining copper tubing. This type of joint is typically associated with larger pipes and mechanical applications where disconnecting and reconnecting components is necessary, such as in some industrial contexts. Flanged joints involve two pieces of metal with flanges that are bolted together, and while they provide a strong connection, they are not practical for standard copper tubing applications which usually require more flexible, lightweight, and secure connections.

In contrast, welded, soldered, and threaded joints are all suitable methods for connecting copper tubing. Soldered joints are particularly common as they allow for a secure seal that can withstand plumbing pressures and is relatively easy to perform in the field. Welded joints can also be used, particularly in systems that require high durability and resistance to leakage, while threaded joints are typical in fittings and connections requiring disassembly. This clear distinction helps to understand the specific applications and limitations of flanged joints in relation to copper tubing.