Which plumbing fitting is used to connect pipes of different diameters?

The fitting used to connect pipes of different diameters is a reducer. Reducers are specifically designed for this purpose and come in two types: concentric and eccentric. A concentric reducer maintains a circular shape and is ideal for vertical transitions, while an eccentric reducer is used for horizontal installations and helps to maintain fluid flow by aligning the tops or bottoms of the pipes.

In plumbing systems, the need to transition from a larger pipe to a smaller pipe (or vice versa) is common, especially when adjusting flow rates or connecting different sections of a piping system. This is where reducers play a critical role, allowing for efficient connections without compromising the integrity of the system or the flow of fluids.

Other fittings like elbows, couplings, and unions serve different purposes, such as changing the direction of the pipe, connecting two pipes of the same diameter, or allowing for easy disconnection of pipes, respectively. Thus, they do not fulfill the specific requirement of connecting pipes with differing diameters.