There are two basic styles of Airbrush: Single Action and Double Action. These two styles also use different methods of mixing paint: External Mix and Internal Mix. The information below will help you determine which airbrush may be suitable for your level of experience and intended use.
Single Action Airbrush: This style of airbrush is the easiest to use and will provide a quality result for the beginner as well as the experienced user. It does not provide the extremely fine line of a Double Action Airbrush, but nevertheless it can spray a pattern as thin as 1/32" or as wide as 1-1/2". The air and fluid controls are independent of one another. Pressing down on the top button controls a pre-set amount of air. The opaqueness of color and width of line are controlled by an adjustment the user sets at the front of the airbrush. This type of airbrush mixes the paint and air externally which produces a larger spray. Single Action Airbrushes tend to be best for spraying slightly heavier paints, solid coats, stencil work and uniform lines and dots. They also clog less easily than Double Action Airbrushes.
Double Action Airbrush: In this type of airbrush the air and color are both controlled with one button. Pressing down on the button activates the airflow and pulling back controls the amount of fluid. This type of airbrush takes more practice but is useful for very fine lines as narrow as 1/64" and for very careful control of opaqueness. Thus with one control the user can change the width of line and the amount of color applied. This style of airbrush mixes the paint and air internally, providing a very fine spray. The Double Action Airbrush will provide the experienced user the most control and is best suited for freehand detail work.