In all cases, the first two digits of the nozzle number indicate the spray angle (dispersion) in degrees. The last two digits of the nozzle number indicate the size of the orifice, an industry standard designation.
Pressure washersspray water in a V shape from the end of the rod. Each nozzle you add to the end of the rod will spray water in a wider or narrower V-shape, depending on the angle at which it is designed to spray.
For example, an angle of 15° is a fairly narrow V, while an angle of 40° is significantly wider. With a narrower spray (a low-grade nozzle), more pressure is exerted on the spray, but it is spread over a small area. If you have a pressure washer or are thinking of buying one, you've probably noticed that there are all kinds of pressure washer nozzles to choose from. The swivel nozzle provides the extreme pressure of a 0° nozzle with the wide coverage of a 25° nozzle.
If you are buying nozzles for your pressure washer, make sure you get the correct nozzles for your machine.