Spray tips are designated by the spray angle (a narrower angle produces more forces over a small area, which is great for tough jobs but may gouge or strip softer surfaces), and by orifice size.
The orifice size designates gallons per minute flow at 4000 psi.
Using a larger orifice than recommended will cause loss of cleaning pressure.
Using a smaller orifice will mean less flow of water at the maximum pump pressure.
Spray tips are available colour coded by spray angle with quick disconnect ends, or with 1/4" male NPT ends.