Masontops CFK9W Complete Mason Jar Fermentation KitThese mason jar fermenting lids screw directly to mason jars, keeping out air while also letting gases escape so you don't have to periodically burp the jar. Highlights: Mouth Type: Wide Mouth Application: Mason Jars Material: Glass Silicone Wood Works with any wide mouth mason jar Airlocks allow internal gases to escape, eliminating the risk of mold and need for daily monitoring during fermentation Glass weights are made of non iridized soda glass