GB/T 20428-2006

GB/T 20428-2006 specifies the technical requirements, accuracy grades, and inspection methods for granite surface plates used as precision reference planes in dimensional metrology. It is applied in manufacturing, quality control laboratories, and calibration facilities for tasks such as checking flatness, parallelism, and squareness of mechanical components, as well as for supporting gauge blocks and measuring instruments. The standard ensures consistent performance of granite plates in industrial environments where stable, wear-resistant, and thermally stable reference surfaces are critical.