Bar's Leaks. Mixes with all quality antifreeze. Harmless to rubber, aluminum, plastic, and all other metals. Has millions of tiny particles to form a lasting internal and external seal in engine blocks and heads, radiator and heater cores, head gaskets, hose connections, and freeze plugs. No. R6: 5.5 oz. regular size for 4 cylinder vehicles No. C16: 10 oz. large size for 6 and 8 cylinder vehicles or hard to stop leaks in 4 cylinder vehicles