Which fitting is primarily used for making a 45° change in piping direction?

A fitting that is specifically designed for making a 45° change in piping direction is a 45° elbow. This fitting allows for a gradual transition in piping orientation, which can help to reduce turbulence and pressure loss in the system compared to sharper turns.

The 45° elbow is widely used in various plumbing and HVAC applications, providing versatility in layout while still maintaining efficient flow. This fitting is particularly beneficial in instances where piping may need to navigate around obstacles or when a moderate angle is more appropriate than a sharp bend, which would be provided by a 90° elbow.

The other fitting options do not serve the same purpose. A reducer is used to connect pipes of different diameters, a 90° elbow makes a sharp turn, and a cap is used to close off the end of a pipe. Each of these fittings has distinct functions that do not include creating a 45° angle, emphasizing the specialized role of the 45° elbow in piping systems.