This standard specifies the formal dimensions, technical conditions and markings of high-strength washers with specifications ranging from 12mm to 30mm. This standard applies to the steel structure friction type high-strength thread connection pair used in conjunction with GB/T 1228 "High-strength large hexagonal head thread for steel structure".
GB/T 1230-2006 Referenced Document
GB/T 1228 High strength bolts with large hexagon head for steel structures
GB/T 1231 Specifications of high strength bolts with large hexagon head ,large hexagon nuts,plain washers for steel structures