15" Parallel ruler Alvin C-Thru like folding parallel rule has clear blades to easy see and read plan or map. The Parallel Ruler provide a fast, accurate method of drawing lines parallel to any reference line. The parallel ruler has non-skid pads on the back and the blades are undercut and beveled. Use the parallel ruler with pen or pencil. The parallel rules are attached with non corrosive & non magnetic aluminum links. The parallel ruler opens to 3” spacing and also available in 12” length.