2 style radiator caps- where to buy what I need

Never have a rad boil over after you flip the safety lever? I have and it filled the overflow bottle faster that you say "holy ****" Flipping the lever pulls up the lower seal off the neck and depressurizes the rad, and like Toolmanmike stated, it'll boil when the pressure is released if its over 212 at sea level. Its called a safety cap as the main gasket never moves, containing all the boiling coolant to the neck of the rad and the poor overflow tube and catch bottle or your toes.