Reduced Diameter Fitting, also known as a reducing elbow. A type of chemical pipeline fitting used for connecting pipes of different diameters. It is further divided into concentric reducing elbows and eccentric reducing elbows. See pipe fittings.

Diameter reducing pipes are available in materials such as stainless steel, alloy steel, carbon steel reducers, and diameter reducing pipes in 20# steel grades Q234 and Q345, etc.