Hey, I'm doing the same thing. I'm building stocks, too, and I need to decide how big to make the holes. Not too big so they can escape or move freely, but not too small so as to potentially prevent anyone from getting in them who has larger legs. I wish I knew the average diameter of a person's leg (down near the ankle area, because that's where you'd want to settle them in, and that part isn't usually too thick). It'd be nice to determine the diameter that would fit most people's in a snug fit. I actually decided on either a 3 and 1/4 inch diameter or 3 and 3/8 inch diameter, and then just padding the inside. What does anyone else think about those sizes?