International connector backflow preventor

Hi, has any european/dutch any clue what kind of parrallel thread connector is best to buy to connect the pressure vacuum breaker? I bought the watts pvb but have problems finding an correct connector. Most EU connectors use bspp. These dont seem to fit on this model (differnt size). Still from the technical spec i cannot derrive if it is npt or other standard (and which size. The inlet is 1 inch and rectangle at the beginning… but i hope to find a right buy (already 2 wrong buys). Anyone got experience for the right eu connector?

some background info.