Front HS bulkheads enable diff height modification utilizing eccentric bushings. Inside front part gearbox, the diff height has a 2mm modification range in which 3 Dot is for cheapest diff location. The diff height adjustment is an important set-up ability that allows fast set-up adaption for either Carpet or Dirt songs. There is 3 different angle designs for modification of front drive train. Carpet version operates with lower trip height as well as keep the drive shafts straight the differential is devote top spot. Dirt variation runs with top journey height also to keep consitently the drive shafts right the differential is invest reduced place. Fits XB4'21