squares, used on surface plates, provide one of the most reliable 90° reference standards available in the industry today. Work may be placed against the periphery and sighted for checking squareness, right angle by comparison method. Master cylindrical squares are also used for checking the squareness of the vertical axis to the horizontal axis of numerically controlled machining centers. Luthra master cylindrical squares are made of high-quality alloy steel, scientifically heat treated for maximum stability and wear resistance. The periphery is ground between centers straight and round within the tolerance specified for each size, with an extremely fine micro finish.