Covington's magnetic backed dot laps have nickel plated diamond rings evenly spaced across the surface with small interruptions that allow for less loading of disc. Magnetic backed diamond discs are super-fast to change and available in four grit sizes, Extra Coarse-60g, Coarse-100g, Medium-260g, & Fine-360g. These discs have a 1" hole to center on plate. Use in combination with Covington's 18" Flat Lap for optimum performance.