Aluminum 12" architect hollow drafting scale is made from high quality extruded aluminum with ultra smooth edges and photo anodized calibrations making them a permanent part of the aluminum that will never wear or rub off. Calibrations are 16, (1/8, 1/4), (1/2, 1), (3/8, 3/4), (3, 1 1/2), (3/32, 3/16).