So I told the guys to install the threaded female fittings in the wall, instead of a bare pipe like they were going to. This was so I could use a fountain, or also use the threaded return jets. Well now I've realized that the female threaded fittings are different from what they use for return jets, so now I have to make these work. Notice how the thread doesn't go all the way to the end of the jet. I was thinking of just cutting a little PVC spacer to fill this gap?
here is the jet, notice how it's not threaded all the way:
here is the fitting I have, notice how the threads go to the end:
here is the usual fitting, notice the gap between the threads and mating surface: