Eccentric Reducer: An eccentric reducer is also known as welded eccentric coupling. It allows for welding a significant pipe to a more compact pipe having an offset center line. The offset of the center line within an eccentric reducer is; Offset = one/two x (Largest ID - Smallest ID) Particularly http://rylangvjwj.fitnell.com/27276969/welded-fitting-fundamentals-explained