The Rubi Tools Stone Cup Wheel 4" (Model #31921) is a high-performance diamond grinding wheel designed for professional use on natural stone, granite, marble, and cured concrete surfaces. It features spiral-shaped diamond segments that efficiently evacuate debris during buffing, ensuring smooth operation and optimal performance. This cup wheel is compatible with most portable electric grinders and polishers, thanks to its standard 5/8" thread connection. It can be used for both wet and dry applications and operates safely at speeds up to 15,000 rpm. The tool is engineered for vibration-free use, making it ideal for detailed grinding and shaping tasks such as creating bullnose or demi-bullnose edges.