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 long-term repeated use. Use single-seal valve principle, this principle can effectively cut off the outdoor air oxidation of the fermentation medium. The fermentation effervescent lock can be used for canning, wine making, beer brewing, sauerkraut and kimchi fermentation to meet your daily fermentation needs. Package contains 2 pieces of airlock, 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 images , please excuse me.