trying to remove tub spout adapter from threaded copper

I need to replace an adapter that is screwed onto the end of the supply pipe, onto which my old spout fits with a friction fit. I can see a couple threads, so if I remove the adapter, I will have 3/4" male threaded pipe to mount a standard spout onto (I can't find spouts to match the old one).

From the wall, it's 1/2" copper, then a unit is soldered on: a short sleeve, then a hex nut, then the 3/4" threaded part.

Here's my problem: the adapter won't come off. Part of the problem is the adapter is round, thus difficult to grip. The other part is it seems to have bonded to the threads. I've tried WD-40 soaking. There is a greenish chalky substance on the exposed threads; is there a certain solvent I should use?

WD40 isn't a penetrating oil designed to help release anything. Get something like PBlaster or just some penetrating oil. It's possible someone soldered that adapter in place, even if it is threaded.

That green chalky stuff sounds like corrosion from the copper pipe. I agree with using PB as a penetrant which may do the trick. Usually, if I run into a problem of a metal fitting or nut that doesn't want to budge I warm it up a bit with a torch... and be VERY careful with the fire. Usually a good pair of channel lock pliers or pipe wrench will get it off with no problem.

How about a picture before you tear something apart. Friction fit spouts did NOT have an adapter.

Thanks for all responses. I finally decided to just cut the adapter off and go with a more standard spout mounting onto the 1/2" pipe directly.