Ball end sheet?

[Jony]

Ok, here's a puzzle...

I'm just building up my new ZX-5 and I've got a foam sheet that doesn't seem to be used anywhere. It's grey foam with little annular shaped cuts stamped into it, so you can pop out little foam donuts.

What's it for?! It's labelled as ball end sheet in the parts list, which suggests it's something to do with the ball ends, but what?

Or can they be used to build a pinion gear which, otherwise, seems to be missing from my kit