I had tried to thread them together without the poly washer, and they still wouldn't mate. I think the permanent washer that was previously installed was ever so slightly too large (in diameter) as to keep the threads on the female regulator coupling from sliding over it. However, at the Praxair...
Went to Praxair this morning and boy were those guys helpful. Apparently once in a blue moon these co2 cylinders show up that have a small extension screwed into the front (see photo). This part threads into the inside of the valve and comes out with an allen wrench. Once removed, my regulator...
It's definitely not reversed threaded, and as far as I can see has the same thread pitch. I guess I'll just have to make a trip to Praxair to tomorrow to see what the pro's think - 6-pack in hand ;)
So I just bought a Midwest Supplies dual draft kit for my mini fridge conversion. I found a screaming deal locally for a filled 20lb co2 tank ($70) at the local fire extinguisher store. The problem - no matter how hard I try, I can't get the regulator assembly to mate to the threads on the tank...