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 to the 60-liter CO2 bottle. 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 part of the bottle compartment shell must be modified to allow the bottle to fit. Efficient and economical: With this adapter, you can continue using your original CO2 cylinders, avoiding the inconvenience 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. Note: Light reflection and different displays may cause slight color variations between the item and the image. Measurement error allowed is +/- 1-3 cm.