I use Badger airbrushes and I can't help you with the parts (why am I even answering this post???
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I tend to agree with both SaltyDog and plasticmod992. You should use the thinnest paint and the lowest air pressure that you can, but you need to find the setting that works best for your airbrush, experience, and paint type. If it takes 30 psi then it takes 30 psi. I spray at between 10 and 15 psi, but I can't paint a thin line for anything. It isn't an issue with my brush or paint or air though, it's just plain me! I guess what I'm trying to say is that the key to painting thin lines is lots and lots of practice!