Diameter of Shaft Under Flywheel is the diameter, of the part of the crankshaft under the flywheel, the distance across the shaft that passes through the center of the shaft is 2R (twice the radius). And is denoted by Ds. Diameter of Shaft Under Flywheel is usually measured using the Millimeter for Length. Note that the value of Diameter of Shaft Under Flywheel is always positive.