Compatibility: fits f many stard CO2 cylinders that have the conventional trapezoidal thread TR21-4. After installation, now you can also use CO2 cylinders from previous versions, compatible with f water aerats DUO, Art Terra. High-quality material: our CO 2 adapter is made of high-quality brass, is rust-proof or abrasion-resistant or high strength, has higher safety, is not easy to damage has a long service life. Easy to install: one end of the quick adapter is connected to the Duo water carbonat 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). F DUO 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 economical: with this adapter, you can continue to use your iginal CO2 cylinders save yourself the hassle of exchanging in the business the cost of changing CO2 cylinders. Now you can also use CO2 cylinders from previous versions. Please note: Befe purchasing, please make that your CO2 cylinder including the valve is iginal (not Quooker), otherwise the Quick CO2 adapter may not be screwed far enough to wk in the new soda machine. Col: 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 different displays may cause the col of the item in the picture a little different from the real thing. The measurement allowed err is 1-3cm.