I create my cabs using CBS dichroic 90 COE glass. These particular pieces are a combination of colors so you do not receive the one in the picture. They are backed in black for fantastic light reflection of colors. Each cab is hand made so they may not be perfectly round in shape. You can choose your size in mm and all of them are 6 mm thick in the center. You can choose the particular size that you are looking for. I have used these in metal clay jewelry and inclusions in other fused glass designs,