Hello

I am thinking of upgrading the crank on an old bike to 105 so i need an octalink BB. I took out the square taper BB in my bike (this was replaced 2 years ago, now it is a BB-UN54) On the BB i saw the usual markings (BB-UN54, 68, BC 1.37x24) then where on other BBs there is a number like 113 or 118, I read D-EL. What does this mean? What BBs are compatible with my bike? Is there a way to use a different number or are they completely not compatible?

Thanks

Your current bb length is irrelevant for a new 105 octalink crankset. The correct BB length for that crankset is a 109.5 such as the BB5500/BB7710/BB7700. Your frame is a 68mm, english threaded according to your current square taper crankset. You will have no problems finding a crankset and BB that will fit.

Octalink bottom brackets came in only two spindle lengths, 109.5 mm for double cranks and 118.5 mm for triples, so there isn't much difficulty telling what you need.

Just be aware that there are two families of Octalink bb's, v1 and v2. The v1 is for most of the road Octalink cranks (including 105), v2 is for most of the mountain cranksets (XTR uses v1). Octalink v2 is available in 113 and 118 spindle lengths, that may be what is confusing you.

Just for posterity, the XTR Octalink V1 was also available in 112.5mm or 116mm... But you want the 109.5mm road bottom bracket as stated.