There are two types of reducer fittings – Concentric and Eccentric.
A concentric reducer joins the tube sections on the same axis. They connect unequal size pipes that have a common centerline and are used for TC transitions in vertical tubing.
Concentric Reducers have different size ends to mate hose or tubing of different diameter that joins tube sections on the same axis. Since virtually all piping systems go through changes in diameter either in the run or at the equipment connections, a reducer serves the dual purpose of changing the piping diameter and at the same time that of handling the expansion, misalignment or vibration problem.
Eccentric reducers are also called bell reducers, they have two female (inside) threads of different sizes with centers so designed that when they are joined, the two pieces of pipe are not in line with each other, but they can be installed so as to provide optimum drainage of the line.
This fitting is designed with the smaller outlet off center to the larger end, allowing it to align with only one side of the inlet. The reducer fittings are designed to be welded with ease and offer superior strength and leak resistance.