Compatibility: fits many standard CO2 cylinders that have the conventional TR21-4 trapezoidal thread. After installation, you can now also use CO2 cylinders from previous versions, compatible with DUO, Art and Terra soda machines. High-quality material: our CO2 adapter is made of high-quality brass, is rust-free / durable / 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 connects to the Duo soda machine, and the other end of the TR21-4 to the 60-liter 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 bit of the bottle chamber container must be cut away 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 store and the cost of exchanging CO2 cylinders. Now you can also use CO2 cylinders from previous versions. Note: Before purchasing, please make sure that your CO2 cylinder including the valve is original (not Quooker), otherwise the Quick CO2 adapter may not screw in 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 to differ slightly from the real thing. The allowed measurement error is +/- 1-3 cm.