My new Lucas ammeter arrived with three brass nuts on each of the two studs - and with the two brass washers each side between the top two nuts.
I have some vague memory from fifty years ago that you should never touch the top nut on an ammeter stud. Which would lead me to place my cable eyelet between the bottom two nuts.
But I could also see a logic to putting the eyelet where the two washers currently are, then using the the bottom two nuts as a fastening nut and a locknut.
Obviously there were no instructions in the box so I'm not sure what the designer's intentions were...
The 2 nuts nearest the bakelite base of the unit are there to hold the guts tight inside the unit.
The other nut furthest away from the base clamps the wire terminal firmly against the middle nut.
Thereby not disturbing the guts.