[mylesdw]

It looks like you have the male/male adapter the wrong way around. The sender nut screws onto the straight thread side (it is a BSP thread). The ridge on the bulb just sits on the edge of the adapter. I have seen a thin copper between the bulb and the adapter but mine seals just fine without it. For a neat job you can buy an ordinary NPT/AN adapter and have the AN end machined. I can give more details if you are interested.