Im confused. Im going to buy a shimano hollowtech bottom bracket to fit a deore crankset onto a frame that takes a 73mm shell, because the frame im swapping out from takes a 68mm shell and therefore it wont fit…or does it?
The adverts ive read for the hollowtech say they fit 68 and 73mm. Ive never fitted a bottom bracket before, so excuse me for being thick, but how can the one bottom bracket fit both sizes? I dont want to buy the wrong thing online, or indeed buy anything at all if it turns out they are interchangeable, which is why im asking for help from someone who knows what theyre talking about.
Can anyone explain this to me?

The bb will be supplied with 3 spacer rings. 73mm shell -one spacer on drive side. 68mm shell- two spacers on drive side and one on non drive side. Spacers are 2.5mm thick, that accounts for the 5mm difference.

So yes, the one from your old frame will fit, but discard one plastic spacer from each side.

Hi,
Oh, riiiiight, i see now- they get measured across the way, not up and down ha ha ha. What a **** i am!
Sorry for taking so long to get back to you guys on this, but we had a big power cut followed by internet dysfunction. Thanks a lot for helping out and taking the time to explain that, lads. Nice one.