This is a set of optional ST Racing Concepts Aluminum Rear Hub Carriers, and are intended for use with the Traxxas Slash 4x4. These rear hub carriers are CNC Machined from high-grade aluminum, and feature a set-screw over hinge-pin design to secure the hub carriers on the hinge-pins. This design prevents pre-mature wear by forcing the hinge-pins to rotate in the suspension arms instead of the aluminum hub carriers. These parts increase durability, while adding an awesome factory look to your Slash 4x4. Note: The set screw in the rear hub is intended for use ST3640RS and ST3640RBK lock-nut style rear outer hinge-pins only. Set screws are not used in the hubs with kit type hinge-pins.