This document describes the design of a rigid flange coupling. It consists of two flanges, one keyed to the driver shaft and the other to the driven shaft. Bolts and nuts are used to couple the flanges together. Design considerations include the diameter and key dimensions of the shafts, dimensions of the hub and flanges, number and diameter of bolts based on shaft diameter, and stress calculations. Rigid flange couplings are used to connect shafts, allow for some misalignment, reduce shock transmission, and transfer power between components.