Go to your scrap bin and look for some good material. The size you need depends on how large of a bangle you are making. A.4-6" diameter disc or square should work. The thickness depends also upon your chuck jaw depth and the size you want. In this one I am using a chunk of Mulberry I harvested last fall the thinnest part was about 1" thick. I also made one with an unused sgmented ring I had glued up already. so you can make your own out of smaller scraps too. Go crazy! I found one side that was somewhat flat, then marked a square and cross-cut the wood to get a square(ish) block of wood. then marked a rough center and drilled a hole large enough for a worm screw for your lathe chuck. then cut the corners off to make it a little easier and safer when you start roughing it to shape.