The fermentation airlock is made of high-quality polypropylene and the stopper is made of food-grade rubber, suitable for fermenting food. The airlock can be used for preserving, wine making, beer brewing, and fermenting sauerkraut, satisfying daily fermentation needs. Simply press the stopper onto the carboy, insert the airlock into the stopper, pour water into the airlock, and cover with the lid to complete setup. The airlock simplifies fermentation by effectively isolating air to prevent oxidation and allows the fermentation process to automatically release gas at normal temperature without manual intervention. Size: Stopper: 17 x 23 x 26mm, Check valve: 17 x 1cm Color: Clear Material: Plastic Package Contents: 4 x Check valve 4 x Stopper Only the above package content, other items not included. Note: Light and display differences may cause slight color variations between the image and actual item. Measurement error is +/- 1-3cm.