This nozzle has a Castle shaped tip. Castellations are added to the tip to protect the needle (that protrudes from the center) from damage, without the castellation the needle is more exposed. Castellations can catch over spray and it can build up on the inside of the air-cap. If paint builds up too much it can bend the airflow and the spay pattern becomes distorted. Ultimately the paint flow can become completely blocked. This phenomenon of paint build up is more rapid in water-based paints due to the larger pigment particles and the fact that they dry so fast. Be sure to use 50496A Acrylic Paint Thinner to clean out wet paint. If the paint has dried use 50497A Acrylic Airbrush Paint Cleaner to clean your nozzles. Blowing the thinner/cleaner through the open side port where your color cup or bottle would be can do this. You can also soak your nozzle in Acrylic Cleaner.