Just a quick question. I may be buying a new frame soon that uses a mid BB. My question is if I take the bearing cups off my american BB bearings, would it work with the mid BB shell? It seems the only difference is that american BB's use bearing cups and mid BB's dont. Im just not sure if that's the only difference.
Im just looking to move on to a lighter frame that isn't 10 years old and I finally found a frame with the same geometry as my STA, but I probably won't be able to afford it if I have to buy cranks too(my cranks use a 21mm spindle so there aren't any mid-BB kits that fit it :()

yes, mid is american without the cups.

cool, thanks, I just wasnt sure if there was some other small difference that I wouldn't find until Im building the new frame.

yes, mid is american without the cups.
ONLY if you have bearings for a 19mm spindle. The bearings for a 22mm or 21 mm spindle in an Amer. BB have a larger outer diameter & won't fit in a Mid BB frame. You need Mid BB bearings specific to a 22mm or 21mm spindle.
-Bill

cool, thanks. I guess Ill have to order bearing then. My spindle is 21mm.

21mm?

21mm?

this is common on cheaper 3pc crank sets like redline monster cranks and similar ones.

I'm pretty sure that those are 20mm (which, conveniently for Spanish users, is the standard bearing size).

my bad, it is 20mm. I dunno why I type 21.

20....21 its all the same.

(any gay if its not 19.)