This standard specifies the type and size of the threaded connection ports of hydraulic components. This standard applies to the oil ports of hydraulic components with working pressure not greater than 40MPa threaded connection.
GB/T 2878-1993 history
2012GB/T 2878.1-2011 Connections for hydraulic fluid power. Ports and stud ends with metric threads and O-ring sealing. Part 1:Ports
1993GB/T 2878-1993 Fluid power systems and components Ports. Ports. Dimensions and design