Compatibility: Suitable for many standard CO2 cylinders with traditional trapezoidal thread TR21-4. After installation, now you can also use previous versions of CO2 cylinders, compatible with water aerators DUO, Art and Terra. High-quality materials: Our CO2 adapter is made of high-quality brass, rust-resistant/wear-resistant/high-strength, with higher safety, not easy to damage, and long service life. Easy to install: One end of the quick adapter is connected to the Duo water carbonator, and the other end of the TR21-4 is connected to the 60L CO2 bottle. You must first remove the pink part from the bottom of the soda machine (pull it out by pressing the pin). For the new version of DUO and ART machines, a small piece of the shell of the bottle compartment must be cut off to insert the bottle into the compartment. Efficient and economical: With this adapter, you can continue to use the original CO2 cylinder, saving the trouble of business exchange and the cost of replacing CO2 cylinders. Now you can also use previous versions of CO2 cylinders. Please note: Before purchasing, please make sure your CO2 cylinder (including valve) is original (not Quooker), otherwise the quick CO2 adapter may not be screwed deep enough to work in your new soda machine. Color: Red Material: Metal Package Contents: 1 x CO2 Quick Adapter 1 x Sealing Ring Only the above package contents, other products are not included. Note: Light reflection and different monitors may cause the color of the item in the picture to be slightly different from the actual item. The measurement allowable error is +/- 1-3 cm.