SAFCO Mayline 42" parallel straightedges are perfect for engineering and construction applications. Every SAFCO parallel ruling straightedge begins with a durable, black phenolic laminate base with a transparent blade for see-through registration and fine line quality. This straitedge is designed with retractile, metal ball-bearing rollers built right into its base. They literally float over the drawing surface. These metal rollers are constructed of chrome-plated brass and are perfect for vellum, paper, and other media. Above-board mounting hardware included. SAFCO parallel straightedges are made in the USA. FREE GROUND SHIPPING TO 48 LOWER US STATES.