Suitable for fermenting vegetables, sauerkraut, or beverages, Econo Lock Airlock creates closed fermenting system when paired with stopper and proper container. Unit allows CO2 to escape but does not allow air back in to contaminate fermenting products. Consisting of 3 plastic pieces that come apart for cleaning between uses, Econo Lock Airlock fits Rubber Stopper # 6 and reCap Pour Caps to turn any mason jar into fermenting vessel.