Brass pipe fittings are typically used for carrying water, chemicals, flammable gases, slurries, and other plumbing substances. Pipe fittings made of brass come in a wide range of shapes and thread sizes to connect, adapt, or control any liquid or gas in pipes.
Brass, an alloy (primarily) of copper and zinc, is one of the most common forging materials used for making fittings.
As an alloy of copper and zinc, brass is compatible with copper, and manufacturers produce many common plumbing fittings with the material. Solder adheres as well to brass as it does to copper, so the fittings are usually molded with slip joints so you can solder them to the pipes.