The fermentation airlock is made of high quality BPA-free polypropylene and the stopper is made of food grade rubber, which is a good and helper for the fermentation food. Brewing airlock can be used for preserving, wine making, beer brewing, fermenting sauerkraut, kimchi that can satisfy your daily fermentation need. Simple to press the stopper onto the carboy, insert the beer airlock to the stopper, pour some water into airlock and cover the lid to complete all operations. Brewing airlock makes easier for the fermentation caused it could effectively isolate the to prevent oxidation and allow the whole fermentation process to be automatic fermentation and exhaust at normal temperature without manual control. size: Stopper:17x23x26mm, Check valve:17x1cm colour:clear Material:plastic Package Contents: 4 x Check valve 4 x stopper Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is 1-3cm.