This item is a which is perfect for and . It can create a closed system that discharges carbon dioxide and prevents oxygen and harmful from getting in and it lets gas out and to keeps air from reaching the or . With one way exhaust water sealed , it can effectively prevent back-flush into the chamber during ambient changes in the room. Feature - Color: Transparent - Material: PP - Size: 3.8 x 3.8 cm ( W x H) - Perfect for , , cider, and secondary . - Isolate the air from the / , discharge carbon dioxide and gas, prevent flying into the / and harmful getting in. - One way exhaust water sealed check valve. Prevent back-flush into the chamber during ambient changes in the room. - Easy to use. Fill water into the exhaust valve, insert to the cover of barrel or rubber plug on the of the container, cover with the lid. - Standard size , fit any , cork, cap, plug, bung, or a grommet with a 3/8 inch hole. Warm tips: - Please use boiled water to boil and the air lock before you using it. And clean it with water after each using. - Please allow 0-1cm error due to manual measurement. Package list: 3 x