The Carbonation Cap is designed to fit most screw top plastic bottles allowing you to pressurise your bottle of beer with CO2. It is made from stainless steel and has a ball lock fitting on the top.
You will need a keg charger or CO2 cylinder along with a ball lock gas connector to use it, sold separately.
The Carbonation Cap is often used to fill a bottle from the keg and then pressurise so that it doesn't go flat - great for taking beer to parties.
Note: product may vary slightly from photo shown.