The Grommets are used with an airlock on top of your fermentation receptacle. When in use with airlock, the grommets maintain a perfect airtight seal and ensures the gas produced in the container can escape. This seal will keep bugs, bacteria, and oxygen from getting into your fermenting product. These are the same ones that fit in our 8 Gallon Fermenting Bucket. The Grommets are made with high quality precision in Italy. We warrant our products in the event that they arrive damaged or defective - Covered under our 30 day hassle free replacement program!