Xray XB4 Rear Suspension Arm.

XB4 rear lower suspension arm made from super-tough, high-tech composite material gives a perfect balance between reliability and performance. The suspension arm is rigid enough for a responsive feel and extreme durability. This  arm is suitable for most track conditions, especially medium- and high-traction tracks. Intelligent arm design allows for variable positioning of the rear shocks. Depending on track conditions, the rear shocks can be installed either in front of or behind the rear shock tower, and the rear shock tower can be placed either in front of or behind the bulkhead.

Hard material is for Medium-High Traction Tracks.

Graphite material is for High-Mega High Traction Tracks