Dimensional Tolerances of Concentric and Eccentric Reducers (ASME B16.9) The ASME B16.9 standard specifies dimensional tolerances for factory-made wrought butt-welding fittings, including concentric and eccentric reducers. These tolerances ensure uniformity, accuracy, and compatibility across various piping systems. Below is a detailed breakdown of the tolerances applied to concentric and eccentric reducers as per ASME B16.9.