[SantaFe66]

You're right about it being two different threadings. One side of the fitting is straight threads and that goes into the adapter I have in the manifold. The other side is pipe threads and the nut on the sender screws on to that. There is only one way for this to fit together as you can see from the picture I attached (whoops, guess it's too big for this, go to my profile and it's the first picture).

Problem is, the nut that's on the sender doesn't bottom on the adapter fitting so the sender moves up and down and won't seal. It looks like there should be some kind of washer in the sender but I don't know what that would be. There is a shoulder on the bulb of the sender and the adapter will only go on one way. The inside of the adapter has been machined out to fit over that shoulder.

Paul