I just ran across two 3 gallon corny kegs with very strange lids and can't find anything about them on the internet. They say "Firestone/Spartan" on the kegs and have ball lock gas in and liquid out posts. However, the lids are like a gas cap or radiator cap, not the standard corny keg oval lid. The lids are round with a gasket on the underside and two metal tabs. The tabs fit into two slots in the keg top and the lid is then twisted closed seating the gaskets. The round lids also have a pressure relief valve in the center. Anyone know anything about this style of keg?