Item Surface Plate Long Form Calibration Certificate No Material Granite Application Grade Laboratory Color Red Edge Style Flat Flatness 0.000050 in/0.0012 mm Grade AA Length 12 in Surface Size 12 in x 12 in 300 mm x 300 mm Thickness 4 in Standards ASME B89.3.7 2013 U.S. Federal Specification GGG-P-463c Surface Size (In.) 12 in x 12 in Surface Size (mm) 300 mm x 300 mm 12 in