From the point of view of saving material and reducing mass, the cross sections of the shaft are equal strength. But from the point of view of processing technology, the shape of the shaft is indeed the simpler the better. Simple shaft manufacturing saves labor, heat treatment does not deform, and has the potential to reduce stress concentration.

When deciding the shape of the shaft, under the premise of assembly accuracy, we should not only consider saving materials, but also consider the convenience of processing and assembly.