Generally speaking brass is between 60% Cu — 40% Zn and 70% Cu — 30% Zn, sometimes added with 1,2% Tin or up to 4% Lead. In California no more than 0,25% Lead is allowed.
There are other special mixtures, but then you have to think about coins, guns and marine use. Not the type of brass we are speaking about.
@ Giorginetto, why do you want to know this?