Provides formulas, on the basis of infinite life, for the design of rotating steel shafts which are subjected to torsional, bending, and axial-tensile loads. It does not apply to shafts specially developed and tested in laboratories or in the field and to shafts for specific applications. A method of establishing a 'trial' diameter, an iterative method of calculating minimum diameter, details of the characteristics of motor controllers and torque-limiting devices, and three worked examples are given in appendices.