Airbrush guns are classified using three main characteristics that relate to how the airbrush functions. The trigger mechanism, which is where the airbrush is controlled, is either single action or dual action. The feed system refers to how the paint is fed into the airbrush. There are gravity-, siphon- and side-feed airbrushes. The mix point, which is either internal or external, is where the paint and airstream meet.
When choosing an airbrush gun, it is important to consider what it is going to be used for as well as personal preference. Single-action triggers are cheaper and easier to use than double-action triggers. They work by expelling the air and paint simultaneously in a fixed flow. Double-action triggers have two separate actions to control the airflow and the flow of the paint. These triggers allow for more artistic versatility.
A gravity-feed airbrush gun has its paint fed by gravity, whereas a siphon-feed gun uses pressure to suck paint into the nozzle. A side-feed gun is a mixture of the gravity- and the siphon-feed systems. Gravity-feed guns have a finer, detailed spray, but siphon-feed guns are easier to control, and side-feed guns can be used upside down. Internal-mix guns are more commonly used than external-mix guns. However, external-mix guns are better if spray consistency is not an issue.