This is a glass cooking tray for your microwave. It is just over 12 inches in diameter. It has 3 partial circles to connect to the turntable driver found underneath. This tray will hold your food and rotate when your microwave is on. You will need to replace this part if it is cracked, chipped, or broken, because that could prevent it from rotating. If your tray is not turning your food will not cook evenly.