Mounted point, 1-1/16″ x 1/4″ a15 (carded). max rpm: 50,510. shank Mounted points and grinding wheels are made from durable, high-grade 60 grit aluminum oxide. perfect for grinding, polishing or deburring ferrous metals or other hard surfaces. for use with 1/4″ (6.35mm) chuck high-speed drills. especially useful where larger wheels will not fit or where small abrasive wheels wear out too quickly.