The air cap is the outermost piece at the front of your airbrush, fitted over the nozzle and needle tip. It shapes and directs the airflow around the nozzle, controlling how the air stream interacts with the paint as it exits.
Different air cap designs produce different spray characteristics. A standard air cap allows the spray pattern to spread naturally in a cone shape. Some manufacturers (notably Iwata with their “Crown Cap”) offer specialized air caps that narrow the spray cone, giving you a slightly tighter pattern at a given distance.
On most airbrushes, the air cap screws on by hand and can be removed for cleaning. Paint can accumulate on the inside of the air cap during use — periodic cleaning prevents this buildup from affecting spray quality.
Don’t confuse with: The needle cap (the protective cap that covers the needle tip when not in use). The air cap shapes airflow; the needle cap just protects the needle.
Related: Nozzle · Needle Cap · Needle Learn more: How to Clean an Airbrush