The Shimano BB-UN300 is a highly reliable square taper bottom bracket designed to provide a smooth and durable interface for your crankset. As the successor to the popular BB-UN26 and BB-UN55 models, it offers a high-quality sealed cartridge bearing system that keeps out dirt and moisture, ensuring long-lasting performance with minimal maintenance. Featuring a strong Chrome-moly (Cr-Mo) axle, this bottom bracket is built to withstand the rigours of daily commuting and recreational riding.

This versatile component is available in multiple configurations to suit various frame and drivetrain requirements. For riders using a full chain case, the BB-UN300-K variant is recommended, while the BB-UN300-E provides the necessary clearance for E-type front derailleurs. While fixing bolts are not included, this bottom bracket remains a staple for those seeking a "set and forget" solution for their square taper drivetrain.

Quick Facts

Feature	Specification
Spindle Interface	Square Taper (JIS)
Bearing Type	Sealed Cartridge
Axle Material	Chrome-moly (Cr-Mo) Steel
Compatibility	Replaces BB-UN26 and BB-UN55
Specialized Variants	-K (Chain case) / -E (E-type derailleur)
Mounting Hardware	Fixing bolts sold separately