The terms “single-action” and “double-action” refer to how the air and paint flow is controlled. Single-action airbrushes spray in a way that’s similar to an aerosol can. Press the trigger to get it to start spraying, while the amount of paint that comes out can be controlled by twisting a knob or screw located near the tip. A double-action airbrush will give you more control, which is essential for working fine lines and to produce the classic “dagger stroke.” This type of airbrush has two trigger movements, and it’s sometimes referred to as “internal-mix” airbrushes because the air and pain mix inside the nozzle.