A Rusto fat cap is a replacement tip for
spray paint cans, similar to a NY
fat cap. Rusto fats create a wide and hard flow of paint, with minimal
overspray.
Graffiti writers use Rusto fat caps with Rustoleum brands of paint, which will not accept the standard fat cap. They are also compatible with certain off-brands of spray paint (but not with Krylon).
See also: fat cap, German fat cap.