Stainless Steel Carbonation Cap, Forced Carbonation PET Bottle Filling CO2 Coupling Cap for Soda Drink, PET Bottles Counter Pressure Bottle Filling Cap with Gasket & O-Rings. DURABLE STAINLESS STEEL CARBONISED CAP：This carbonation cap is a high quality stainless steel carbonised cap that is resistant to corrosion and erosion.
eBay