Every Whipple Supercharger pulley is made of 6061-T6 billet aluminum and anodized for wear and environmental protection. Each pulley is engraved with the running diameter size and state-of-the-art light weight pockets to lower recipocating mass as well as a guard feature to help unwanted belt wandering during hard running. Standard finish is hard coated black anodized. Dimension of each supercharger pulley is based off of the running diameter. *A general rule of thumb is every .125" of pulley change is 1psi of boost. There are no returns or exchanges for used pulleys. **Whipple Supercharger pulleys are specific to the application, do not order this pulley for a different application.Learn More