I've bought some time ago BOC RS 600 Nitrogen regulator from ebay.co.uk. I don't live in UK and there is a different standard for Inlet connectors in my country. I've bought a proper inlet connector from other regulator that will fit nitrogen tanks in my country but I need to thread one side of the connector to fit to the BOC regulator. Maybe someone know what thread is between the Inlet connector and BOC regulator. I asked BOC but they didn't reply. I found some British Standard for regulators but they are pricey.

Here is the regulator and the description says "BS341 no. 3 5/8" RH" for the side of tank.

And the thread that i talk about: