What Bikes Need the Shimano BB-UN300-K 68x122.5mm Bottom Bracket?

The Shimano BB-UN300-K is the long-spindle variant of the BB-UN300, pairing a 68mm English threaded shell with a 122.5mm spindle for applications where additional spindle length is needed to achieve correct chainline. The cartridge bearing construction delivers sealed, smooth rotation in a non-serviceable unit with Shimano's standard sealing quality, and the integrated chain line stabilizer reduces lateral chain movement for consistent shifting performance. The longer 122.5mm spindle is most commonly called for on MTB triple chainring setups or specific road frames where frame geometry pushes the chainrings outboard to clear wide chainstays.

English threaded 68mm shell, JIS square taper interface, aluminum adapters, standard structure. Compatible with all square taper JIS cranks -- confirm that 122.5mm is the correct spindle length for your specific crank model and chainline requirement before ordering, as spindle length selection is determined by the crankset spec sheet and not by shell threading alone. Installation requires a Shimano TL-UN74-S or equivalent splined BB wrench. If you are replacing a worn UN300 or similar cartridge BB and the old unit was 122.5mm, this is the correct OEM-quality replacement.