Item Surface Plate Material Granite Application Grade Inspection Color Gray Edge Style Flat Flatness 0.00012 in/0.0030 mm Grade A Length 12 in Surface Size 12 in x 18 in 300 mm x 450 mm Thickness 3 in Flatness Unilateral Tolerance (In.) 0.00012 Flatness Unilateral Tolerance (mm) 0.0030 Standards GGG-P-463c Surface Size (In.) 12 in x 18 in Surface Size (mm) 304 mm x 457 mm Weight (Kilograms.) 42 kg 18 in Weight (Lbs.) 32 lb