Rotor T47 30mm EXTERNAL BB STEEL BLACKROTOR T4730 bottom brackets are available for frames with a standard T47 bottom bracket shell. As always, the bottom bracket cups are precision machined in our Spanish manufacturing facility. Rotor's T4730 External uses external cups, measuring roughly 11. 5mm outboard on each side. Rotor's T4730 Internal uses internal cups in which the only outboard piece is the castellated flange, which measures roughly 1. 7mm on each side. Rotor's T4730 Asymmetric