Traxxas optional adjustable suspension arm allows wheelbase adjustment depending on track conditions and driver preference. Forward pivot ball holes increase wheelbase 0.39" (10mm) and rearward pivot ball holes increase wheelbase 0.75" (19mm) over stock control arms Black nylon construction INCLUDES: One each left upper and lower and one each right upper and lower arms two bumper mount spacers and two 4 x 16mm cap screws . Suspension Arms are available separately.