Curious about codes on BB-UN73
 

Hi folks,

I have this BB-UN73 bottom bracket here and where it would sometimes say the spindle width, instead it has: "L<- D-H ->R", on image search I see other 73s that have D-NL instead of the D-H, or a MM1xx size, I haven't been able to figure out what the letter codes mean, anyone know?

Did you look at the tech docs like this?

Ah, no, also wow I'm obviously not versed in Shimano bottom brackets, I thought the one I saw with MM110 meant 110mm spindle, maybe it does connote that but that label is the spindle type apparently, same with D-H, D-NL, etc.I couldn't figure out how to search for this, thanks for the assist.

The D historically means the spindle is asymmetrical, with the Drive side being longer than the NDS. I'm not sure why it's important to designate that on a one-way cartridge unit, however... The NL and H nomenclature might just be part numbers that correspond to spindle lengths.

This is correct.

For Shimano BB, the D-H is the marking for the 115 nominal size, 115.5mm total, 23.5mm drive side, 24mm non-drive. This is based on a 68mm width model.