These are the Traxxas Steel-Spline Constant Velocity Rear Driveshafts for the Slash 4x4, Stampede 4x4, and Rally 1/10. These upgrade driveshafts are great for increasing power transfer efficiency and handling the large amount of torque produced by today's brushless motor systems. And you never have to worry about losing a pin because the U-joint pins are locked in place.