18-Inch Silver Engineer Triangular Drafting Scale from Alumicolor. Made of extruded aluminum to give them strength, but hollow for easy portability and a lower cost. Photo anodized calibrations are part of the aluminum and will never rub off or fade. The finish is smooth and resistant to solvents and cleaners. Standard Engineering calibrations: 16, (1/8, 1/4), (1/2, 1), (3/8, 3/4), (3, 11/2), (3/32, 3/16). For professionals and students.