Square Type Bicycle Bottom Bracket BB UN300 With Hollow Spindle For JIS Square Taper Cranksets, BSA 73Mm Shell, 122.5Mm Spindle, Durable Construction For Smooth Pedaling, Improved Stiffness And Efficient Power Transfer
✔️ Single unit: 73mm shell width, 34.8mm dia, 122.5mm spindle
The BB UN300 bottom bracket is designed for JIS square-taper cranksets, perfect for bikes with a 73mm BSA English shell. It uses a precision-machined hollow spindle to reduce weight and improve stiffness, enhancing pedaling efficiency. It fits a 73mm shell width (2.87in) and 1.37-inch shell diameter (34.8mm), with a durable black finish that resists corrosion. This unit is sold as a single piece for straightforward installation on road and mountain bikes.
✅ Hollow spindle for weight savings and enhanced stiffness (122.5mm length / 4.82in)
✅ Fits JIS square-taper cranksets with 73mm shell width and 1.37in shell diameter (73mm/2.87in; 34.8mm/1.37in)
✅ BSA English threaded shell for easy installation and broad bike compatibility
✅ Durable black finish with corrosion resistance for long life
💡 What is a bottom bracket used for in bikes?
It serves as the bearing housing that lets the crank rotate smoothly while transferring power to the drivetrain. It also helps determine frame compatibility and pedaling feel.
- bottom bracket compatibility with JIS square-taper cranksets - sealed bearings reduce friction and wear - hollow spindle saves weight and increases stiffness - shell width and diameter must match frame specs (e.g., 73mm, 1.37in)