You use diamond discs to grind extremely hard materials. They're made of steel with diamond grains on the edges, so you can grind various types of stone, ceramic, and concrete with it. To enjoy your disc as long as possible, it's important to use the right diamond disc for your job. Because diamond discs are available in various shapes and sizes. What size you need depends on what angle grinder you're using and the job you want to do. With a 125mm diamond disc, you can cut even the hardest material in half.