Compatibility: Fits many standard CO2 cylinders with conventional trapezoidal thread TR21-4. After installation, you can use CO2 cylinders from previous versions, compatible with water aerators DUO, Art, and Terra. High-quality material: Our CO2 adapter is made of high-quality brass, rust-proof, abrasion-resistant, and high strength, offering higher safety, durability, and a long service life. Easy to install: One end of the quick adapter connects to the Duo water carbonator, and the other end with TR21-4 fits the 60-liter CO2 bottle. Remove the pink part from the bottom of the soda machine by pressing the pin to pull. For new version DUO and ART machines, a small part of the bottle compartment shell must be cut to allow the bottle to fit inside. Efficient and economical: With this adapter, you can continue using your original CO2 cylinders, avoiding the inconvenience and cost of exchanging cylinders. Note: Before purchasing, ensure your CO2 cylinder including the valve is original, otherwise the Quick CO2 adapter may not screw in far enough to work with the new soda machine. Color: Red Material: Metal Package Contents: 1 x CO2 Quick Adapter, 1 x Sealing Ring Only the above package content is included; other products are not included. Note: Light reflection and different displays may cause slight color differences between the item and the image. Measurement allows an error of +/- 1-3 cm.