Shimano BB-UN300 Bottom Bracket - English | 68 x 110mm Spindle - Square Taper JIS

Shimano BB-UN300 Bottom Bracket - English | 68 x 110mm Spindle - Square Taper JIS Shimano

Shimano BB-UN300 Bottom Bracket - English | 68 x 110mm Spindle - Square Taper JIS

Shimano BB-UN300 Bottom Bracket - English | 68 x 110mm Spindle - Square Taper JIS

Shimano logo

Which Bikes Need the Shimano BB-UN300 68x110mm Bottom Bracket?

The Shimano BB-UN300 in the 68mm English x 110mm spindle configuration is a cartridge bearing square taper bottom bracket built for bikes where a shorter spindle produces the correct chainline -- primarily road and hybrid frames with double chainring setups where the shorter 110mm spindle positions the chainrings correctly relative to the dropout centerline. The integrated chain line stabilizer keeps lateral chain movement in check for more consistent shifting across the cassette or freewheel. Shimano quality seals and cartridge bearing construction deliver smooth, reliable rotation and long service life in a fully sealed, non-serviceable unit.

English threaded 68mm shell, JIS square taper interface, aluminum adapters, standard structure. The BB-UN300 is available in multiple spindle lengths -- 110mm, 113mm, and 122.5mm -- so confirm your required spindle length before ordering, as the correct length is determined by your crank model and desired chainline rather than bike type alone. Compatible with all square taper JIS cranks. Installation requires a Shimano TL-UN74-S or equivalent splined BB wrench. For the mechanic or rider who needs a trusted, no-fuss OEM-quality square taper replacement in the 110mm spindle length, the BB-UN300 is the go-to choice.

Sale
$15.99
$15.99 $18.00
Shipping calculated at checkout.

2 in stock

  • Orders over $100 ship free!
  • Estimated delivery: Jul 10 - Jul 14

Ask a question

The fields marked * are required.

more details:

Shimano logo

Specifications

  • Model: BB-UN300
  • Interface: Square Taper JIS
  • Shell: English threaded, 68mm
  • Spindle Length: 110mm
  • Bearing Type: Cartridge (sealed, non-serviceable)
  • Structure: Standard
  • Adapter Material: Aluminum
  • Installation Tool: Shimano TL-UN74-S or equivalent splined BB wrench

FAQ

How is 110mm different from 113mm in practice?

A 110mm spindle positions the chainrings 1.5mm closer to the frame centerline compared to 113mm. This affects chainline -- the alignment between chainring and cassette. Some double chainring road cranksets produce the best chainline with 110mm, while others call for 113mm. Always reference your crank manufacturer's recommended spindle length.

Does this BB fit a 73mm shell width?

No. This variant is spec'd for 68mm English threaded shells only. For 73mm shells, you need the BB-UN300 in a longer spindle configuration designed for that shell width. Check your frame specification before ordering.

Will a JIS taper BB work with ISO taper cranks?

No. JIS and ISO square tapers use different angles and are not interchangeable. Installing an ISO crank on a JIS spindle (or vice versa) will not seat the crank correctly and will damage the taper. Confirm your crank's taper standard before purchasing.

Best For

Road and hybrid cyclists with English threaded 68mm BB shells running double chainring square taper JIS cranksets that require a 110mm spindle for correct chainline.

Shimano BB-UN300 Bottom Bracket - English | 68 x 110mm Spindle - Square Taper JIS Reviews:

You may also like