to make the settings with small round tubes and solder claws to
If you mean you’re going to individually solder prongs onto
Boy oh boy, that’s a lot of solder joints all close together.
This would be the time to use diestruck findings. Or a cast strip.
But generally about sizing, it depends on whether your settings will
be straight or tapered.
If straight, make the tubing the size of the stone or slightly less,
recess the prong into the tube enough so that the centerline of the
prong is just a bit outside the girdle of the diamond.
If tapered, you want the stone to fit inside the prongs so that after
you cut the seat down with a bur you will have enough prong above the
stone to properly bend over. Personally, on something this small I
like to have a lot of prong above the stone because short stubby
things do not bend so well, I like the extra leverage of a long
prong. But on a tapered setting, viewed from above you should not
see the base of the setting after the stone is set.