F;
Those sound like the right sizes.
"Years ago" there was a specific adapter for that, which held the 'bulb' & allowed It's fiting to tighten against it, sealing both the threads & the bulb. Otherwise it would leak around the line.
The smaller fitting may not be a tapered thread which NPT is.
The threads in the 'larger'(elec sender) are a tapered (NPT) thread, probably 1/2".
Someone here will have one "laying around"......
