The Hole Core Buddy hole coring system cores holes up to 10 inches in diameter and eliminates the need for bulky drill rigs and works with tools already owned. It is sold as a kit and ready to adapt to the contractor's drive motor, such as a 9-inch grinder. Premium hole core drill bits designed for the kits have a special connection system that help self-align the core bit and the drive shaft. U.S. Saws. 866-987-7297.