Bike rear derailleur pulley fits for bike of 12T and 8, 9, 10, 11 speed. Product Style: 12T. Item Type: Bike Rear Derailleur Pulley. Feature: 1. Aluminum Alloy Material: All aluminum alloy material, strong and impact resistant, riding more assured, the layer is anodized, effectively protecting the aluminum alloy body, anti corrosion and anti oxidation.