Avid Titanium Upper Arm Balls for the Xray X4 are 4.9mm in diameter and a lightweight replacement for the kit steel part XRA303232. On this part, we have moved the ball up 0.25mm to maintain the same roll in the car as you would have with the heavier steel parts. Like all of our titanium parts made here at Avid RC, they are of the highest grade billet 6Al-4V Titanium to ensure the best strength possible.