Shimano un55 square taper bottom bracketthe shimano un55 square taper bottom bracket has super accurate bearings for smooth operation and improved durability with a durable and hard wearing sealed cartridge this bottom bracket is maintenance free and keeps dirt water and mud from penetrating the unit featuresa good quality bottom bracket for traditional chainsetssuper accurate bearings for smooth operation and improved durabilitydurable hard wearing sealed cartridge bottom bracket with squ