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 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 it out. 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 hassle and cost of exchanging cylinders. Please note: Before purchasing, ensure your CO2 cylinder including the valve is original (not Quooker), 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 the color of the item in the picture to vary slightly from the real thing. Measurement may vary by +/- 1-3 cm.