All AAU1365 are the same OD. However, at some point in the distant past, the manufacturers started making this bearing with a reduced width outer race. It was probably an economy measure, and they also did it on later wheel bearings too.
The problem was, when this narrower bearing was used in 4-syncs, the absence of that part of the outer race allowed 1st gear to move over too far, and the box did not work properly. However, this design would work in 3 synhro transmissions.
So we found ourselves having some stock that worked in 3-syncs and some that worked only in 4-syncs. Hence, Seven (and no one else) created the AAU1365-3 and AAU1365-4 distinctions. After a while, the original bone-headed decision was overruled, and all new production became full width again, but we had the -4 still attached to the part number for some time. It has now faded into the annals of Mini trivia.
There were actually two (2) bearings used prior to AAU1365. Very early 3-syncs through September 1964 used a slightly smaller bearing, and to make matters worse, in the old days there were kits to change from the integral cone synchro rings to conventional type rings, and some of these kits changed the main shaft and therefore the type of bearing needed. These bearings are now obsolete.
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