Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (68mm) (115mm)

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Shimano BB-UN300 Square Spindle 68mm 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: 68mm
Spindle Lengths: 107mm, 110mm, 113mm, 115mm, 117.5mm, 118mm, 122.5mm
Color: Silver
Weight: TBD

This product was added to our catalog on August 11, 2020

J.C. Bryant
Verified Owner
Saturday, Apr 22 2023 (about a year ago)
Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (68mm) (107mm)
Shimano makes a lot of bad products these days but they’ve outdone themselves this time. Shimano used to make great square taper bottom brackets but this one feels incredibly cheap right out of the box. I had trouble getting this installed. The splines fit poorly with my Shimano bottom bracket tool that has worked for literally every other Shimano cartridge bottom bracket I’ve used it on. The poor fit means it starts slipping under torque and all it took was a couple slips to significantly damage the splines. I am expecting to return this to performance bike. That is, if I can manage to get it out of my bike. Complete garbage.

As far as I can tell, they haven’t posted specs for spindle length (ie symmetric/asymmetric offset), so good luck getting the proper chain line. Avoid this product like the plague. You’d be better off with literally any other bottom bracket on the market.
Steve H
Thursday, Sep 15 2022 (about a year ago)
Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (68mm) (117.5mm)
I used this to replace a >30 year old cup/cone original BB. I measured the spindle length and ordered the cartridge BB with the same spindle length. But no- it didn't work- the chainline is now too long by about 7 mm which makes a huge difference. I searched the internet and Shimano website to find anything explaining how far to the right the spindle extends, because spindle length alone does not tell the whole story. No luck. Ordering a second BB now and hoping it works.
Verified Owner
Monday, Jun 14 2021 (about 3 years ago)
Shimano UN300 Square Taper English Bottom Bracket (Silver) (BSA) (68mm) (122.5mm)
My 2017 Trek FX.2 had +7000 miles on it and was time to replace most of the moving bits. Replaced the bottom bracket with a UN300. The original bracket (VP BC-73) was 68 x 121.5 for JIS square-taper cranks. The UN300 was slightly longer (122.5 vs 121.5 mm) and changed the chain-line, requiring that the front derailleur needed adjusting. All-in-all, the UN300 easily fit into the bicycle frame and appears to be better quality then the original bracket.