Product Features: Material: Aluminum alloy, Copper Color: Gold; purple silver Subject: TR21-4 Function: Connect the soda cylinder with TR21-4 thread to DUO, TERRA soda machines with quick-connect cylinder Features: 1. Fits many standard CO2 cylinders with the conventional trapezoidal thread TR21-4, bottles up to 60 liters and 425g CO2. Made from durable and extra lightweight aluminum. Environmentally friendly, durable, high safety, rust-free, and sustainable. 1. Remove the pink part from the bottom of Terra Water Dispenser by pressing the pin according to instructions and pulling the unit downward. Compatible with DUO and ART bubblers, a small piece of the housing must be cut out in the cylinder compartment so the cylinder can be inserted into the compartment. 2. Screw our quick adapter firmly onto the conventional TR21-4 valve with the installed flat gasket. Perfectly fits our 425g CO2 cylinders but also works with cylinders from other manufacturers like Crystal 2.0, Penguin, Cool, and Aqvia. IMPORTANT: If the adapter cannot be screwed onto the CO2 bottle's handle, this cylinder is not compatible with this adapter. If you have any questions, we are happy to answer them. 3. Insert the 425g cylinder into your Soda DUO, Art, or Terra and secure it by pulling down the quick connector and pressing it into the water disperser until the unit clicks into place. IMPORTANT: The hex screw (safety valve) on the TR21-4 valve must be positioned so it extends out from the unit and NOT sideways or into the storage compartment. Why choose us? What if you only have a blue CO2 bottle but are too lazy to go out and refill? Or are there no gas stations nearby? The improved quick adapter from WADEO, specially developed for carbonated water heaters with pink CO2 bottles. If you only have the blue CO2 bottle, take this adapter home, you can refill the blue bottle directly, then add the adapter, and then use it on Terra/Duo/Art series SodaStream soda machines.