Compatibility: Fits many standard CO2 cylinders with conventional trapezoidal thread TR21-4. After installation, you can also 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 portion of the bottle compartment shell may need to be modified to allow proper insertion of the bottle. Efficient and economical: With this adapter, you can continue using your original CO2 cylinders, avoiding the inconvenience and cost of cylinder replacements. Please note: Before purchasing, ensure your CO2 cylinder including the valve is original (not Quooker), otherwise the Quick CO2 adapter may not screw in sufficiently 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 variations between the item in the picture and the actual product. Measurement allows an error of +/- 1-3 cm.