Bottom Bracket BB-UN55 BSA 73-122.5mm

The Shimano BB-UN55 is a square-taper cartridge bottom bracket built to the English-threaded standard, offering a dependable balance of quality, value and durability. Its hollow spindle design pairs with JIS square-taper cranksets, giving riders a straightforward, long-lasting foundation for everyday drivetrain performance across a wide range of bicycle builds.

Built with a cartridge bearing assembly, the BB-UN55 threads into a 73mm English (BSA) bottom bracket shell and uses a 122.5mm spindle, providing consistent operation and efficient power transfer. Crankarm fixing bolts are not included, so riders should source them separately when installing this bottom bracket on compatible frames.

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