Abstract: A drive shaft (41) is disclosed of the type having first and second sets of axially-disposed external crowned splines (39 and 43) for transmitting torque between first and second sets of internal straight splines (37 and 45). The sets of internal straight splines are relatively transversely disposed such that the drive shaft is disposed during operation at a running angle (A) relative to the axis (79) of the internal splines. Each of the external crowned splines includes a pair of tooth flanks joined at a root radius having a radius (R). The root radius (R) is related to the running angle (A) of the drive shaft by the equationR=C/A.sup.2In this equation, C is a constant for the particular drive shaft design, and is determined empirically to yield a minimum circular clearance between the external spline and the adjacent internal spline.