30mm Superball Damper feet for 40 Profile

I was wandering around my local "The Range" store when I stumbled across these little superballs. You know the sort; you throw them hard, and they bounce higher than a house (not too difficult, as my house doesn't bounce), and then ricochet off about 200 miles to where you'll never find them again.

They're about 30mm in diameter (just under an inch and a quarter in old money), and seemed to me to be be a much neater solution than squash balls. They also have the added advantage that they're d