Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (73mm) (122.5mm)

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Shimano BB-UN300 Square Spindle 73mm Bottom Brackets


  • Fits JIS square-taper cranksets
  • Crankarm fixing bolts sold separately
  • Hollow spindle

Frame Interface: BSA/English Threaded
Spindle Interface: Square Taper JIS
Bottom Bracket Shell ID: 1.37
Shell Width: 73mm
Spindle Lengths: 113mm, 118mm, 122.5mm
Color: Silver
Weight: TBD

This product was added to our catalog on July 31, 2020

Paul Kirchgessner
Verified Owner
Monday, May 8 2023 (about a year ago)
Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (73mm) (113mm)
Though I had nothing to compare to, the bottom bracket did not seem to rotate as easily or as smoothly as expected upon receipt. The part failed 8 months / 450 miles later. Not sure if it was defective or not suited to more demanding cycling. This replaced the 34 year old Shimano BB on a 1989 Specialized Rock Hopper.