ST Racing Concepts Traxxas TRX-4M Brass Front Steering Knuckles. These optional steering knuckles are intended for the Traxxas TRX-4M. Made from brass, each knuckle is CNC machined for perfect fit and finish. Increase the durability, lower CG and move the weight forward in your TRX-4M with the ST Racing Concepts Brass Steering Knuckles. Package includes two steering knuckles.