Thread size on fuel filter

[Rodeo Joe]

I can,t find the answer to this anywhere , does anybody know what tread size the fittings are that screw into the filter housing. I measured the 2 blanked off ports opposite the main feeds but it seems to be 12 and a bit mm or nearly 1/2" so none the wiser. I need to put on a spill pipe into it and don't know what size to ask for
Any help appreciated