This part of GB/T9125 specifies the structural type, dimensions and tolerances, materials, manufacturing and heat treatment, inspection and acceptance, product quality certificate, marking and marking, protection and packaging of fasteners for Class series steel pipe flange connections. requirements. This section applies to the steel pipe flange connection fasteners (including hexagon head bolts, fully threaded studs and nuts) specified in GB/T9124.2 and GB/T13402.