Regarding the OEM pulleys that came on the Sram RED rear derailleur the other day

↑I mentioned that the retainer had some clearance,
but that's because the bearing ball size is larger.

On a separate note,

a customer came in who had replaced
the upper and lower pulleys on a Shimano RD-5800
with aftermarket ceramic bearing ones,
and the lower pulley had stopped moving during a ride
(the image shows the upper pulley),
so they slightly loosened the pulley fixing bolt
and managed to get it rotating enough to make it to our shop.


This pulley has no distinction between upper and lower,
neither has floating function,
and since there's no designation for the lower pulley, there's no left-right orientation either.


When I peeled back the seal, it looked like this.
Then I removed the lower pulley


and the broken retainer and bearing balls
came spilling out everywhere.
The bearing balls were tiny—about the size of sand grains.



The ball race wasn't eaten away by corrosion or anything,
so it seems the retainer ring deformed and then collapsed—that was the cause of the explosion.