The banjo bolt with thread M14x1.5 and the respective banjos are used as hose connectors for filter heads and prefilters.
To get a banjo bolt/banjo sealed, you need 3 washers al-m14.
With the double banjo bolt the in- and outlet of filter heads can be used double. E.g. for the connection of a pressure gauge you need the double banjo bolt together with a banjo (ring-m14-4) for the hose s-pa-4 leading to the pressure gauge sog-anz-profi.