The outside diameter of the hollow shaft must be at least . Typically, this value would be rounded up to the next larger standard size. Rounding the outside diameter to the next larger size will increase the shaft's polar moment of inertia, and the larger will ensure that the actual shear stresses are less than the allowable stresses.
If the inside diameter is to be of the outside diameter, the maximum inside diameter would be . The inside diameter should be rounded down to the next standard size. Rounding up would be incorrect for the inside diameter as this would tend to reduce the polar moment of inertia for the shaft, leading to stresses higher than the allowable stress in the shaft.
Finished