not sure the actual size on each needle for the Paasche, but they are small, med and large needles.
1 is the fine needle, usually too small to effectively spray model paints through because of pigment size.. from what I hear it's better for spraying inks and the like.
3 is your baby, the med needle should be all you need to do a model... anything should spray through it (any model paint that is
) and you should be able to do sufficient detail, and/or coverage that you would need with it...
5 is the big daddy, for spraying that mural on the wall. Not very good for modeling unless you are building a 1/2 scale Spitfire or something like that...