ST Racing Concepts Traxxas TRX-4M Brass Differential Cover. This optional differential cover is intended for the Traxxas TRX-4M. Made from brass, this cover is CNC machined for a perfect fit and finish. Increase the durability, lower CG and move the weight forward in your TRX-4M with the ST Racing Concepts Brass Differential Cover. Package includes one differential cover with hardware.