Size of tank threaded fitting?

[JBSSRT-4]

Can anyone tell me the size of the threaded fitting on nitrous bottles? Not the size of threaded fitting you connect the line to, but the size of the larger connector on the tank valve that you connect the line adapter to.

You know....the size of the large connector used to fill the tank?

(of course I am assuming they are all the same)

I have two 10 lb. bottles of different manufactures and they use the same size line adapters. I just need to know what the standard size is on the bottle valve.

Thanks