I already did man.
Look, i took a photo. Right and left are the same 73 mm 'mtb' bb, left has a 2.5 mm spacer on it. Middle is a road bb. Does this make it clear? They fit the same cranks. The mtb ones are 10 mm wide, the road ones are 12.5 mm wide. There are also bbs for italian shells, which are 11.5 mm wide because italian bb shells are 70mm. They all fit the same cranks.

Btw 'mtb' bbs will often say 68/73 because you can run those 2.5 mm spacers and use them in a 68 frame.