What type of joint is commonly used for connecting two pieces of copper pipe without adding additional fittings?

The type of joint that is commonly used for connecting two pieces of copper pipe without adding additional fittings is a capillary joint. This joint is created by heating the joint area to the melting point of solder, allowing the solder to flow into the space between the two joined pipes through capillary action. This method provides a strong, durable connection that is ideal for copper piping systems.

In typical plumbing installations, a capillary joint is preferred because it results in a seamless appearance and maintains a clean installation with minimal additional materials required. It leverages the properties of solder to ensure a watertight seal and is especially effective in situations where space or fittings may be constrained.

The solder joint generally refers more broadly to any joint made by melting solder, but the capillary action is specifically the mechanism that allows solder to fill the joint when heating copper pipes, making this term particularly relevant to the question.