The Mr. Pen Professional Metal Compass with Wheel and Lock for Geometry is built for precision work across math, geometry, art, drafting, and drawing—especially when you need consistent, larger circles. Creates circles up to 18 inches: Includes a universal adapter and extension beam for bigger circle work Spring bow head + center wheel: Designed for precise control and stable performance Quick-setting adjustment: Push-button adjustment helps you set measurements faster Helps prevent slips: Mechanism helps prevent unintentional leg movements Premium quality: Built for reliable, repeatable results Included accessories: 10 extra leads , spare needle , screws , and a screwdriver Easy to store and carry: Packaged in a clear, reusable pouch