OPC Bottom Bracket (Hanger) Bearings 9-10-12-loose

[Phil Fink]

I see that bottom bracket bearings with retainers are cheaper by the box; (10 may seem like a lot, but that's 5 bike sets).
I have some pre-balloon motorbikes with 5/16" x 10 each bearing retainers, and understand that long ago (pre-BMX) the industry may have conformed to 5/16" x 9 each(?). I have also seen 5/16" x 12 each offered. Is/was there a technical reason for the changes/differences? I understand that 9 bearings could be 10% cheaper than 10, and may allow more room for grease, yet the loose bearings crowd might say that the more bearings the better - suggesting 12's as the best of the retainer options(?).
Then there is the even-versus-odd argument, that an even number of bearings might have pairs of bearings perhaps opposing each other, under certain forces or stresses(?) - but that seems too complicated for my simple mind.
I have seen an article on an English-speaking DIY website, that indicating that the bearings (and cups) have (unstated) dimensional differences, and the road bike expert said they are not interchangeable. I don't see the differences on the used parts that I have - perhaps he was referring to 1970's Japanese bikes(?).

 

[Bicycle808]

The cups are different, as are the cones. Basically, most cranks and BBs are 24tpi and use the 10x5/16" caged bearings. Chicago Schwinn and very early Mongoose bikes run 28tpi with BBs that take the 9x5/16" caged bearings. Take makes a nice BB set for 24tpi cranks that takes the 9-ball bearing. In any case, you're going to want to use the right cups with the rest of the BB set for best results. The threading will HAVE to match on order to work but ppl often run the wrong cups with the right BB set and wonder what went wrong.

I have no clue where the 12x5/16" cages come in.

My advice? If you're a Schwinn guy thinking original cranks, stock up on the 9 ball sets. If you're any other type of guy, stock up on the 10 ball sets. And yes, more balls is another but less balls is cheaper, night I think Schwinn weren't with a different set up b/c they were always running proprietary stuff in hopes of keeping their customers captive to the Schwinn dealer.