ALVIN Paral-Liner Mobile Parallel Straightedge Rigid phenolic construction with a black satin finish. Mobile straightedge affords frictionless operation through the floating action of the nylon rollers mounted on the blade. The rollers retract at a touch, securing the blade for accurate drawing. Plexiglas edges are elevated to prevent ink smears and steel ball-bearing pulleys provide smooth movement. Comes with all mounting hardware and installation instructions. Parts Diagram