This tool room grade "B" Granite Plate has a bilateral accuracy of plus or minus .00015" total instrument runout for precision measurements from a common surface base. Granite Plates are harder than steel, non magnetic, least responsive to temperature changes, practically maintenance free and won't corrode like steel. Weighs 234 lbs. Grizzly G9656 - 24" x 24" x 3" Granite Surface Plate, No Ledge