ISO 13948-1:2015

ISO 13948-1:2015 specifies dimensions and requirements for mechanical, threaded connections used on diesel fuel injection pumps and fuel injectors for the connection of low-pressure fuel, lubrication oil or air supply.
Five types of threaded connections (types A to E) are described in this part of ISO 13948. Type A is commonly used for both pumps and injectors, while types B to E are for diesel fuel injection pumps only.
NOTE:         Low-pressure connections to fuel filters are covered in other International Standards; see the Bibliography. High-pressure end-connections for pumps and injectors are covered in ISO 2974