Item features: Material: Aluminum alloy, Copper Color: Gold; Lilac silver Thread type: TR21-4 Function: Connects CO2 cylinders with TR21-4 thread to DUO, TERRA, and ART soda machines with quick-connect cylinder system Properties: Fits common CO2 cylinders with standard trapezoidal TR21-4 thread, compatible with bottles up to 60 liters and containing up to 425g CO2. Constructed from durable, lightweight aluminum alloy. Environmentally friendly, robust, safe, stainless, and long-lasting. Compatibility instructions: For use with DUO and ART carbonators, a small section of the housing in the cylinder compartment may need to be removed to allow proper insertion of the cylinder. Installation steps: 1. Remove the pink piece from the bottom of the Terra water dispenser by pressing the pins as shown in the included instructions and pulling the unit downward. 2. Screw the quick adapter, with the flat seal inserted, securely onto the standard TR21-4 valve. Fits perfectly on 425g CO2 cylinders, including those from various brands. IMPORTANT: If the adapter does not screw into the CO2 cylinder valve, the cylinder is not compatible. 3. Insert the 425g cylinder into your Soda DUO, Art, or Terra machine and secure it by lowering the quick-release lever and pressing the cylinder into place until it clicks. IMPORTANT: The hexagonal safety valve (on TR21-4) must face OUTWARD from the device, not sideways or inward. Why choose this adapter? Ideal for users who have a blue CO2 cylinder but want to avoid frequent refills or lack access to refill stations. This upgraded quick adapter enables compatibility between standard TR21-4 threaded CO2 cylinders and selected Sodastream series machines. Scope of delivery: 1 x Quick Adapter