Explain why are hollow shafts are preffered to solid shafts for transmitting torque?

Let me list down a few of the advantages first.

• In comparison to a solid shaft, a hollow shaft is of less weight, for a given length and diameter. This is pretty obvious and wont be requiring any further explanation. Moreover it’s a good idea to go ahead with hollow shafts, if we our emphasis is on weight reduction and cost-cutting.
• Hollow shafts are much better to take torsional loads compared to solid shafts. As shown in the figure, shear stress in a “shaft subjected to torsion” varies linearly from zero at the center to the maximum at the boundary. Inside a solid shaft, most of the material experiences / carries a shear stress whose value is much below the maximum shear stress [Interior portion of the shaft]. But at the same they are adding to the weight, without contributing much to the capability of the shaft to carry torsional load.
• Hollow shaft has a greater Strength to weight ratio.