Bottom bracket BSA 122.5/73mm BB-UN300 square taper

The reliable and maintenance-free SHIMANO BB-UN300 is a square taper bottom bracket with a 73 mm BSA thread and 122.5 mm axle length. It offers smooth rotation, secure fit, and long service life for everyday use, commuting, and worry-free kilometers.

Why choose BB-UN300?

• Quality/Performance-class bearing – stable, quiet, and durable operation.

• Chainline stabilizer – optimizes chainline and improves shifting and drivetrain efficiency.

• Multiple construction options – Standard, E-type, and chain case compatibility.

• Durable adapter – aluminum adapter adds extra stiffness and secure tightening.

• Easy installation – traditional BSA thread, generally fits 73 mm BSA frames, square taper cranks.

Technical details

• Type: Bottom bracket bearing, square taper

• Model: SHIMANO BB-UN300

• Thread/shell: BSA, 73 mm

• Axle length: 122.5 mm

• Construction options: Standard / E-type / chain case

• Adapter material: Aluminum

• Compatibility: SQUARE TAPER CRANKS and frames with BSA 73 mm bottom bracket shell