Elastomeric expansion joints, unlike piping expansion joints of other materials, can be manufactured with concentric or eccentric tapers, transitioning from a larger diameter on one side and smaller on the other. These expansion joints are normally hand-built on a mandrel and not of the molded variety. The low volume requirements and nonstandard lengths do not support the high cost of mold tooling.
Before moving forward, it is important to define and clarify the difference between concentric and eccentric tapered reducers:
The concentric design is where the center of each flange is concentric or in line with each other
The eccentric design is where the center of each flange is eccentric or offset with each other