Once you try lacto-fermenting in mason jars with these airlock lids, you may never go back to ceramic crocks, even for large batches! This simple efficient system works with wide-mouth jars (3⅜" outer diameter) to produce delicious and nutritious probiotic foods. You provide the wide-mouth jars, and this kit provides 4 easy-to-use BPA-free airlock lids with silicone gaskets, 4 sure-grip glass weights, and one 12" bamboo tamper. Fedco Seeds coordinator Bernice Nadler has been singing the praises of this kit since 2019: “Other fermentation methods, such as in crocks, often develop surface mold that has to be scraped off. This has never been an issue with my airlock kit. It has expanded my culinary repertoire.” We trialed these airlock lids against a hip-looking waterless competitor, but we found that the waterless lids often leaked fermenting fluid onto the counter. We never should’ve doubted your suggestion, Bernice! Kit developed by a small family-owned business in Pennsylvania. NEW!