Front HS bulkheads enable diff height modification using eccentric bushings. Inside the front component gearbox, the diff height has a 2mm modification range through which 1 Dot is for top diff location. The diff height modification is an essential set-up ability that enables quick set-up adaption for either Carpet or Dirt songs. You will discover 3 different angle designs for modification the front drive train. Carpet variation operates with minimal journey height and to keep consitently the drive shafts appropriate the differential is devote top destination. Dirt variation runs with top journey height and also to keep consitently the drive shafts appropriate the differential is invest lower spot. Fits XB4'21