This nifty gadget lets you carbonate beer, soda, water, wine, etc. in a standard plastic PET soda bottle (20 oz., 2-liter, 3-liter, etc.).  Threads onto the top of the bottle, and allows you to connect to your CO2 system via a standard ball lock gas disconnect fitting.  In addition to force carbonating, you can also fill PET bottles with keg beer or other previously carbonated beverages, and use this product to seal for traveling, or even to replace some of the carbonation lost in the filling process.