ROTOR UBB 4630mm Threaded Bottom Bracket - SteelROTOR UBB 4630mm Threaded Bottom Bracket Steel You, or more specifically, your choice of frame, motivated Rotor to address challenges related to bottom bracket installation and durability. They embraced the task to improve upon so called bottom bracket standards to give you the UBB4630. Crafted from 7000 series aluminum alloy, the UBB4630 uses a threaded sleeve to lock both cups in place without having all the locking effort rely on the press fit