For sale is an NOS RC6 13lbs radiator pressure cap by AC Delco. GM 850800 part#. This item fits various models of GM cars, including Chevrolet Buick and olds. Most notably this radiator cap is correct for 1958-1959 fuel injection Corvette. This is the older style cap without the metallic cover having the graphics. If you desire the newer style, I have one of those in a separate sale as well.