Shimano BB-UN300 British Thread Bottom Bracket Made with Shimano’s usual exacting standards, the BB-UN300 Bottom Bracket is an excellent option for bikes that have British threaded bottom bracket shells and chainsets with a traditional square tapered spindle fitting. Made into a one-piece unit, this bottom bracket keeps dirt, mud and water away from the sealed bearings to offer durability, corrosion resistance and low friction operation. The threaded construction installs easily without the need for any fiddly adjustments, and the narrow body of this unit means that it won't hinder gear and brake cables that are being routed internally through the frame's bottom bracket shell.