a very intriguing question that may not have an answer, page-3

Yeah, common misconception is that the bearing is the axle on the side member, with the axle fixed to the wheel.
It should be fairly obvious that the bearing is actually the wheel on the axle, and the axle is fixed to the frame. The upright support on the canopy is fixed to the side member by drilling through the side member and also through the rear axle, thus fixing it in place. The front axle is also fixed to the side member with a primitive dowel that is not visible from the side elevation view.