These are available in a variety of sizes:
3/4″ BSPM x 1″ BSPF
3/4″ BSPM x 3/4″ BSPF
1″ BSPM x 1″ BSPF
These are often fitted between the end of the hose and the nozzle so that it can be twisted around to the correct orientation; however, this can also be fitted in other locations, such as on the end of the hose next to the pump, etc, in special circumstances.
Unless specifically stated, these may be made of Aluminium, Mild Steel or Brass according to what material is available at the time of manufacture (all these materials are suitable for use with diesel). If you are using Adblue, Water or some other Chemical then you are likely to need Stainless Steel.