airbrush needle help

Where's MikeV when you need him??

Looking at the shape of those two needles, one thing comes to mind: As the needle is pulled back from the nozzle it acts like a throttle and the distance between the needle and the nozzle controls the amount of paint flow. The long, tapered needle on top is going to give a gradual increase in paint flow as it is pulled back and probably won't reach full flow until it gets near the back of the travel. The needle on the bottom will unseat relatively quickly and give full paint flow after very little travel and then pulling the trigger back further won't affect the amount of paint.

My guess is that the long tapered needle on top is the one that would be used for fine lines wheras the one on the bottom would be used for large area coverage, but it's just a guess.

MusicCity is right.

The reason for the different needles is so that they can handle different mediums sprayed through the airbrush. The #1 (fine) needle and tip are for the thinnest pigment mediums such as inks, dyes, thinned acrylics and enamels.
This needle will produce the finest lines but it is more prone to clogs because of it's small size and sharp taper of the needle.
The #3 (medium) needle and tip are for slightly heavier lines and thicker mediums such as acrylics for T-shirt painting, etc.
The biggest needle, #5 needle and tip are for thick mediums such as stains for wood, latex paints, and whatever else you may want to spray through it.
It can also be used for spraying the widest pattern for coverage of larger areas as the opening is fairly big.

The ones you will want for modeling are mainly the #1 and the #3 and I would experiment with both to see which produces the spray pattern you are looking for.
I always used the #1 with my Paasche VL when I had it years ago.

The needles are identifiable by the marks at the back end of them.
The #1 needle has one groove cut in it, the #3 has three grooves cut into it and I believe the #5 has a '5' engraved into it, although it has been a while so I am not positive.

I hope this helps.

Mike