The General Tools Heavy Duty Circle Cutter can produce precise circles in sheet metal, brass, copper, soft steel, aluminum, plastic, wood and composition materials. Durable body of heat-treated tool steel. Adjustable to various diameters by included hex wrench. Only safe to use with drill press running at less than 500 rpm. Included blade (#55 Blade) and 1/4 in. pilot drill bit (#5/6/55 Drill) are replaceable. Diameter range: 1-3/4 to 7-7/8 in. Shank size/shape: 1/2 in./round. Includes: #55 Blade, #5/6/55 Drill (1/4 in. pilot drill bit) and hex wrench.