Excel 55778 - Deluxe Model Railroad Reference Rule. - Constructed of 12 1/2 inch long non-glare gold anodized aluminum with black calibrations in N, HO, O, and G(1/24) scales., 64th and mm along with a guide for converting decimal equivalents to drill sizes for small screws. The black photo-anodized calibrations will not fade or chip when cleaned with solvents.