What fitting would you use to ensure a pipe can join at a right angle?

The fitting that is used to ensure a pipe can join at a right angle is the pipe elbow. A pipe elbow is specifically designed to change the direction of the flow in a piping system by allowing pipes to connect at angles, most commonly at 90 degrees, which corresponds to a right angle. This is critical in both plumbing and various piping applications where space constraints or design requirements dictate that the flow needs to redirect sharply.

Pipe reducers are utilized when there is a need to connect pipes of different diameters, effectively reducing the size of the flow path. Pipe unions serve to connect two sections of pipe together but do not alter the angle of connection, making them unsuitable for joining pipes at right angles. A piston ring compressor is unrelated to piping and instead is a tool used in engine assembly, further emphasizing that it is not applicable in this context. Thus, the pipe elbow is the appropriate choice for creating a right-angle connection between pipes.