Most airless paint sprayers have interchangeable tips, often two or three of them. These tips are usually marked with a three-digit code. Generally, the first number is half the width of the spray fan that tip produces from a distance of 12 inches, and the second two numbers are the size of the tip opening, or orifice, in thousands of an inch. So for example, a tip marked “517” produces a 10-inch spray of paint and has a .017-inch opening.  The right tip for your job depends on the type of paint being sprayed and the size of the job itself. If you are painting a large, flat surface, such as a wall or fence, you’ll want a tip that produces a wider spray of paint, whereas painting a lattice, furniture, or other detailed work calls for a narrower paint fan.  As for orifice size, the thicker the paint, the larger the required opening. As a rough guideline, thick exterior latex paints require an orifice of .015 to .019, oil-based paints and interior latex need an orifice of .013 to .017, enamels work best with an orifice of .013 to .015, and thin stains, sealers, lacquers, or shellac need a small orifice of .009 to .013.