What type of fitting is typically used to connect two pipes of different diameters?

The fitting that is typically used to connect two pipes of different diameters is a reducer. A reducer is specifically designed to transition between two sizes of pipe, allowing for a smooth flow path and minimizing turbulence that could occur during fluid transfer. By using a reducer, a plumber can successfully join pipes of varying dimensions while maintaining the integrity of the plumbing system.

Elbows, while important for changing the direction of a pipe run, do not serve the purpose of connecting different diameters. Couplings are used to join pipes of the same size together, making them unsuitable for varying diameters. Caps are designed to close off the end of a pipe and do not facilitate connections between two separate pipes. Thus, the reducer is the appropriate choice for this application.