The Energon Pub

And I can't figure out what the peg-holes on the sides of his upper arms are for. The ones revealed when you move the tank treads.

They don't seem to be used in any of his six modes. You can sorta-kinda stick his guns in there to give him Starscream-styled arm guns, but the wheels on his forearms keep it from really working out.

So what are they for?