This is the Traxxas Inner Drive Cups (2)
Drive Cups, Inner (2) Revo (steel constant-velocity driveshafts)/ screw pin, M4/15(2) (for use only with 5333R adjustable wheelbase rear suspension arms)
These rear drive cups are engineered exclusively for use with the combination of Traxxas steel constant-velocity driveshafts (#TRA5451R) and the adjustable wheelbase rear suspension arm set (#TRA5333R) on Revo. These specially designed drive cups help keep the shafts securely in place throughout the huge range of suspension movement and extreme driveshaft angles allowed by the adjustable wheelbase suspension arms.
Note: These drive cups should not be used with standard wheelbase rear suspension arms.