Alvin #505V drafting compass includes ruling pen and beam bar extension. Designed with fiberglass ring head and pivot design for smooth, firm adjustment. Accurate center wheel adjusts quickly and easily for drawing circles up to 20" diameter. Features split leg design that accepts interchangeable pen, pencil, and divider parts. Built-in spindle stop prevents overextension. Matte nickel finish resists stains and tarnishing. Slip handle for spare ruling pen. Extra lead, needle point, and bolt.