Fangrui Product Details 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- / 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 ( 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 Cyli