While RPM make's all type's of parts for all type's of RC vehicle...installing them correctly is crucial.

Here's the method I use....Before poping the ball's into the cups I heat them in boiling water. This is to help them re-turn to origianal diameter after strecthing them from installation. The plastic is softer when it commes out of the boilng water. I also install them from the bottom upthat way if they do
stretch it will not pop off from landing hard since the top is still original size.

Just a tip I use on my RPM stuff .....Arm's, ball cup's it work's on all plastic's not just RPM.