gas tank

[Hemi Bob]

I have a question I want to replace my 85 fj1100 gas tank it has a small dent in the side that would require repainting the hole tank.
I have seen in two new tanks for sale from europe but looking at the pictures they bolth have only two holes in the filler area
two to mount the cap. my tank has a third nut just to the left of the filler hole? do we know what this third bolt is attaced to and
do i need it.
thanks
Robert