Front HS bulkheads enable diff height modification utilizing eccentric bushings. Inside front side part gearbox, the diff height has a 2mm modification range which 3 Dot is for cheapest diff location. The diff height modification is a significant set-up capability that allows fast set-up adaption for either Carpet or Dirt songs. There's 3 various angle designs for modification of front drive train. Carpet version operates with lower journey height and keep consitently the drive shafts directly the differential is devote top spot. Dirt variation runs with top journey height and also to keep consitently the drive shafts appropriate the differential is invest reduced place. Fits XB4'21