Compatibility: Fits many standard CO2 cylinders with the conventional TR21-4 trapezoidal thread. After installation, you can now also use CO2 cylinders from previous versions, compatible with DUO, Art, and Terra water carbonators. Premium Material: Our CO2 adapter is made of high-quality brass, which is rustproof, abrasion-resistant, and high-strength. It offers enhanced safety, is not easily damaged, and boasts a long service life. Easy Installation: One end of the quick adapter connects to the Duo water carbonator, and the other end of TR21-4 to the 60-liter CO2 bottle. You must first remove the pink part from the bottom of the soda machine (press the pin to pull). For DUO and ART machines of the new version, a small piece of the bottle compartment shell must be cut away so that the bottle can be inserted into the compartment. Efficient and Economical: With this adapter, you can continue to use your original CO2 cylinders, saving you the hassle of exchanging them in the store and the cost of replacing CO2 cylinders. Now you can also use CO2 cylinders from previous versions. Please Note: Before purchasing, make sure that your CO2 cylinder, including the valve, is original (not Quooker), otherwise, the Quick CO2 adapter may not be screwed far enough to work in the new soda machine. Color: red material: metal Package Contents: 1 x CO2 Quick Adapter 1 x Sealing Ring Note: Light reflection and different displays may cause the color of the item in the picture to be slightly different from the real thing. The measurement allowed error is +/- 1-3 cm.