Premium Quality Material - Our fermenting lids are made of stiff and durable plastic with a leak-proof silicone gasket and waterless airlock valve. Both the fermenting lid and accessories are food-safe, BPA-free and dishwasher safe. Easily separate each part of the fermentation lid for a thorough cleaning, and be confident that your ferment equipment is safe and healthy. Excellent Universal Fit - Included in each package are 1 oxygen extraction pump and 4 fermentation lids for standard wide-mouth Mason Jars (outer diameter of 3.38 inches). This fermenting kit is an ideal starter kit for making homemade sauerkraut, kimchi, pickles and more! Innovative Design - The innovative one-piece waterless airlock valve can vent gas from the jar while preventing oxygen from getting inside. A silicone seal inside the mason jar fermentation lid works with the one-way airlock valve to make the fermenting work done on their own and stop oxygen and any nasty airborne agents from getting in for a successful fermentation. Super Easy to Use - These fermenting kits are perfect for beginners and seasoned pros alike. The silicone valve and seal gasket are easy to assemble and detach making fermentation easier. Check your ferments easily and reseal the lid by simply opening the release valve to release gas and use the extraction pump to pull oxygen out. 100% Satisfaction - Customer Satisfaction is our top priority. If you are not happy with your fermentation lids for any reason, please contact us for a full refund!