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.

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.

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.