Ive just noticed that if I take the hex head nuts off the middle of my crankarms on the hollwtech 2 deore set up Ive got, you can see through the bottom bracket. It is infact, as the name implies, 'hollow'. Do these rather solid and well machined hex head nuts keep the crank arms / chainset on, or are they just dust caps that I can leave off to show off my fancy hollow bottom braket to me mates?!
making it all up as i go along