Vin Table's silicone fermenting and ventilating bungs have created more options for the Winemaker in creating a special blend. This #7 silicone airlock bung is the perfect size for sealing 5.0 gallon (20L) glass carboys. Vin Table silicone bung is highly stable and designed for long lasting, withstanding a temperature range of -100°F to 400°F Tested with Shore Durometer, this bung was graded with a Shore A hardness of 40, so no need to worry about cracking, chafing, mold, and mildew.