The high-quality SHIMANO BB-UN300 square-taper bottom bracket, designed with reliability and smooth drivetrain operation in mind. Featuring sealed cartridge bearings and a lightweight aluminium adapter, it is the ideal solution for mountain, trekking and city bikes requiring a stable crank mounting.
Unrivalled durability and smooth bearing operation
The sealed cartridge design protects the bearings from dirt, water and sand, significantly extending the component’s service life and eliminating the need for frequent maintenance. The precision-machined axle ensures smooth rotation under load and minimises rolling resistance whilst riding.
Smooth gear changes thanks to chainline stabilisation
The use of a chainline stabiliser guarantees consistent and precise drivetrain guidance. Thanks to its robust construction and aluminium bottom bracket shell, the entire assembly offers high rigidity and a perfect fit for a 73 mm frame shell.
Specifications:
| Brand | Shimano |
| Model | BB-UN300 |
| Bottom bracket type | Square Taper |
| Cage width | 73 mm (BSA thread) |
| Axle length | 113 mm |
| Adapter material | Aluminium |
| Design | Cassette-style, with chainline stabiliser |
| Bolts included | None |
| Packaging | Single (BOX) |
| Replacement for model | SHIMANO BB-UN55 |
