Quote Originally Posted by Skullcruncher View Post
Yep the wheels/arm piece.
To clarify, you can't swap CJ & BB's arms, although the wheels/tyres are fine.

Cliffjumper & Hubcap share the same arms, but Bumblejumper's arms will only work with Bumblejumper. Bumblebee's arms will work only with him.

(I'm ignoring the later repaints like Bug Bite for simplicity's sake)