Interestingly I've come across two different thicknesses of spacer that fit into the hub behind the bearing outer...
Both appeared to be standard parts and it makes me wonder whether the metric size bearing was ever fitted as standard...
BSA used plenty of metric bearings in other applications. However, I've not come across any part number differences to infer a change...
If it ever happened I would think it would only be towards the last of the rigid frame models which ended in the early 50s....Ian
1) Take .87mm/34.252thou off each spacer (the spacers or bearing carriers that go between the hub and the cup of the bearing) or,
2) replace with 05079/05185 imperial bearings
The benefit of 1) above is that cheaper metric bearings can be used (now and in the future). The downside is that quite a bit will have been taken off the spacer/bearing carrier.
I haven't measured the depth of the spacer, but my guess is that it cannot be more than 4mm, so taking off nearly a quarter of its depth.
Regards
Pat
ps I wonder why they didn't cut the hub shallower and do away with the need for the spacers?
I machined the hub bearing thrust nut with peg, 15-7049, down a few thou to suit, its plenty thick enough. Anybody with a lathe will be able to do this for you.