The ATD Tools Mini Grinding Discs are for use with ATD-6601 or ATD-6602 disc holders and come in three grains. The aluminum oxide discs are for general metal and woodworking applications when the user needs to sand or break edges or blend surfaces. The zirconia discs are longer lasting than the aluminum oxide option, self-sharpen with use and are for pre-paint surface preparation. The green zirconia discs offer the hardest grain for high-temp alloys, stainless steel and titanium. The self-sharpening grain improves life while it also disperses heat better than other grains. These discs are for sanding, grinding and breaking edges.