Originally Posted by
Iride01
If it's a cartrige bearing or external cups I'd probably just replace the entire BB. If old style separate spindle, bearings and cups, then I'd replace whichever needed it.
However....
Never have I ever had to replace a BB for wear. I have replaced them for other reasons.
And I suspect you have never worked in a bike shop doing repairs. Just yesterday I replaced a BB on a customer's 20ish year old Trek road bike because the axle spun roughly. This was a cartridge unit (a Thun). Until the crank arms were removed it was easy to not notice the wear. Andy