[Lynn Eades]

The wheels all have the same bores. the inner front bearing mounts to a stub axle that is bigger in dia. (50mm) at the inner end. The outer end is 40mm. this is because of the loading as well as the front stub only being supported at the inner end, whereas the other axles are all supported at both ends.
So the o.d. of all bearings are the same. What Richard is saying is that the 50mm bore bearings are cheaper to buy. I think Kevin did the research and turned up spacers to enable the use of the 50mm bore bearings at all locations. The bearings are a standard metric 6000 series ball race. I think all are inter-changeable from the early bren through to the T16. There are some semi thrust bearings in some carriers, and some are fitted with bushes. The rule would be to use the same style of what ever type in each wheel assembly.