This standard specifies the recommended type dimensions for the ends of externally threaded parts such as bolts, screws and studs. This standard applies to standard or non-standard external threaded parts. A designator is specified for each end style and may be used when a threaded fastener specifies an end.
GB/T 2-2016 Referenced Document
GB/T 5276 Fasteners.Bolts, screws, studs and nuts.Symbols and descriptions of dimensions