CO2 Quick Adapter for Duo-Quick Connect QC, Art and Terra, Replacement for CO2 Cylinder TR21-4 Male Compatibility: fits for many standard CO2 cylinders that have the conventional trapezoidal thread TR21-4. After installation, now you can also use CO2 cylinders from previous versions, compatible with for water aerators DUO, Art and Terra. High-quality material: our CO 2 adapter is made of high-quality brass, is rust-proof / abrasion-resistant / high strength, has higher safety, is not easy to damage and has a 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 to the 60 litre 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 shell of the bottle compartment must be cut 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 and save yourself the hassle of exchanging in the business and the cost of changing CO2 cylinders. Now you can also use CO2 cylinders from previous versions. Please note: Before purchasing, please make 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 Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.