Originally Posted by
ThermionicScott
As far as I know, the cartridge bodies all have the same dimensions at the end (OD, edge radius, etc.) Problem Solvers sells a universal replacement cup in each shell width (68mm or 73mm) and it's not specific to the bottom bracket length.
The differing part numbers may indicate whether the left-side cup has a lip on it or not, I much prefer the ones without.
EDIT: I was right! The cup shipped with the 107mm unit doesn't have a lip (it's threaded all the way to the end):
https://www.amazon.co.jp/-/en/SHIMAN.../dp/B008E4KA90
The other cup has a lip on it:
https://www.amazon.co.jp/-/en/SHIMAN.../dp/B008E4KAJA
Interesting. Presence/absence of a lip would explain the different part numbers.
Makes me wonder why Shimano didn't simply use the same left adapter within each size they made (68mm wide, 73mm wide, and 70mm wide), though. The 107mm left adapter is different from the other spindle lengths for each size. Seems to me it would have been significantly cheaper and easier for Shimano to make 3 different left adapters for the BB-UN55 series vice 6.
Seems to me they'd have a good reason for fabricating 6 different parts, given the extra expense involved, rather than 3. But maybe not.