Rotor pf41 steel bottom bracketrotors press fit bottom bracket bearings are compatible with all bb90 press fit system frames that are manufactured to shimano specifications the new advanced non contact labyrinth seals yield a buttery smooth spin with unparalleled protection against dust water and mud ultra rigid plastic caps give high compression and deformation resistance facilitating crisp shifting available with steel or ceramic bearings constructed of cnc machined 7075 aluminium comp