Bottom Bracket BB-UN300 For JIS Square Taper Cranksets, Hollow Spindle With 50mm Chainline, BSA 68mm Shell, 122.5mm Spindle, Fits Classic And Modern JIS Cranks, Crank Arm Fixing Bolts Sold Separately, Durable And Precise

BB-UN300 JIS Bottom Bracket for Square-Taper Cranks (Single) ✔️ 68mm shell width, 50mm chainline, JIS square-taper, 122.5mm spindle

The BB-UN300 is a square-taper bottom bracket designed for JIS cranksets, suitable for classic and modern bikes. It fits standard BSA 68mm shells and uses a hollow spindle with a 50mm chainline, delivering precise alignment and efficient power transfer across rides.

✅ 50mm chainline for balanced power transfer
✅ 68mm shell width matches BSA threaded frames
✅ Hollow spindle reduces weight while maintaining strength
✅ Compatible with JIS square-taper cranksets; bolts sold separately
✅ Durable black anodized finish resists corrosion
✅ High-precision bearings deliver smooth rotation and longevity

💡 What is a JIS bottom bracket used for in a bicycle drivetrain?

A handy piece that connects the crankset to the frame, enabling smooth rotation and stable chainline. - Supports JIS square-taper cranksets and standard 68mm shells
- Helps convert pedal power into drivetrain movement with minimal friction
- Keeps chainline aligned for consistent shifting and performance
- Works with crank fixing bolts sold separately