This airlock is made of food grade PP plastic, it is transparent so you can know exactly when the fermentation has stopped. Without manual control, simple and easy to use, operation, and also can a long-term repeated use. Use a single-seal valve principle, this principle can effectively cut off the outside air oxidation of the fermentation medium. The fermentation effervescent lock can be used for putting canning, wine making, beer brewing, sauerkraut and kimchi fermentation to meet your daily fermentation needs. The package contains 6 pieces of airlocks, suitable for your home brewing needs. Due to factors such as manual measurement and display differences, there may be slight differences between individual products and pictures, please forgive me.