The petcock is 16mm x 1mm. Used on some Husqvarna motorcycles and Puch mopeds. They come in a couple of different different outlet sizes. Either will work but I like the larger which I think is 6mm. I buy mine from Treatland tv out of San Francisco. They are the best to deal with. I hope this helps and good luck.
One other thing, the OEM petcocks are very hard to come by. The packing in them break down after so long. I have rebuilt a couple using the packing from if I remember was from a BSA petcock. Decided it was not the time and effort. I am not all that into having a factory correct bike. And by the way nice survivor.