Carrier Rad Elbow Question

[Bruce Parker (RIP)]

I'm doing some rad work on my carrier and thought it was a good time to plumb the overflow tube I didn't do the first time around. This pic is of the brass elbow that is mounted on the engine cover just to the right of the rad cap. The wide end takes a rubber tube right off the rad cap and the threaded end takes a copper tube running to a water condenser can on the rear deck.

My question is what thread does the threaded end use? It is 1/2" but doesn't match any fittings I have available here in Canada.

Do any UK MLU carrier people know what this thread might be and if there is a source for a fitting I might be able to get?