5\8" and a couple of 3/4". The method used on the pipe makers forum is to tilt the crooked ring and sand the high side on sandpaper on a flat piece of glass or granite, check with calipers, sand, check, sand, check. I tried that and it was a major PITA and was extremely time consuming. This takes less than 5 minutes once the piece is cut on the miter saw and the thicknesses are repeatable. I tried an electric miter saw and two different manual miter saws and none of them would cut the acrylic with parallel sides.