SHIMANO UN55 BB Square Taper Bottom Bracket Review Posted by GiantPandaisy May 16, 2018 in Drivetrain Components Bottom Bracket Fit – 68mm BSA of ENG Sealed cartridge bearings The Shimano BB-UN54/55 Square Taper bicycle bottom bracket gives you reliable strength for square tapered cranksets. Cycling Outdoor Recreation Parts & Components SHIMANO Sports & Outdoors