High-strength structural bolting assemblies for preloading - Part 10: System HRC - Bolt and nut assemblies with calibrated preload High strength bolt: BS EN 14399-10 Nut grade 10 HRD Washer BS EN 14399-5,grade H. The high strength bolt will be black oxide coating. A307 bolts shall be galvanized in accordance with ASTM A153 or European Standard SEE ATTACHMENTS