Riders replacing a worn Octalink bottom bracket on a 73 mm English-thread frame, with a crankset that calls for a 121 mm axle.
The BB-ES300 is Shimano's Octalink bottom bracket for Alivio-level mountain and trekking cranksets. It is one sealed cartridge unit with a hollow steel spindle, a resin left-hand adapter and a steel, phosphate-coated right-hand shell.
This is the 73 mm English-thread version with a 121 mm axle. The axle length sets your chain line, so match it to your crankset as well as your shell: Shimano's chart, for example, pairs the Alivio FC-M4000 with a 118 mm axle.
Hollow Octalink spindle
The 8-splined Octalink interface adds strength and rigidity to the whole assembly, says Shimano.
Sealed cartridge unit
Bearings and spindle sit in one sealed unit that fits and swaps as a single part.
Chain stabilizer
Shimano lists a chain stabilizer for good chain line control.
73 mm English thread
BC1.37 x 24 threading for 73 mm shells, with a 121 mm axle.
Fit
Build and install
Great for
Maybe not for
Confirm the shell width (73 mm) and English thread, then match the axle length to your crankset. This one is 73 mm with a 121 mm axle. Shimano also makes the BB-ES300 for 68 mm and 70 mm shells and in 113, 118 and 126 mm axles, and those are separate parts.
Get the axle length right first
The axle sets how far the cranks sit from the frame, and so your chain line. Shimano's chart pairs the Alivio FC-M4000 with a 118 mm axle and the FC-T4010 with 126 mm, so check what your crankset needs before settling on 121 mm. Shimano's manual also says to grease the body, fit the body first and then the cup, tighten to 50 to 70 N·m, and not to grease a plastic cup. The left-hand adapter on this one is resin.
