Imagine that you are trying to make a wheel. You would most likely lay it on the floor so that you could assemble the spokes in the rim. Now imagine how sore your back would be after making a few wheels in this bent-over position! Fortunately, some bright soul came up with the idea of the hub cradle. It would hold the wheel rim vertically so that spokes could be inserted more easily. The maker could spin the wheel as spokes went in, reducing the amount of bending needed. Much easier on the back, which was good in the days before the chiropractor!