Blue plastic 3/8 inch thick, matte finish on both sides to hold and release clay more easily. .
All production bats are simple flat circles intended for wheel heads with two batpins. Standard drill is two holes 10 inch center-to-center to fit Brent, new Pacificia, Soldner and many others.
The 13 inch diameter is made so that, when used on standard 12 or 14 inch wheel head, 1/2 inch of the bat overhangs all the way around the wheel head, making it much easier to remove the bat from the wheel without disturbing the thrown piece. No more prying, no more broken fingernails!