This solid silicone bung from CellarScience will provide a tight fit and secure seal to your oak barrel or variable volume tank lid. Made from pliable silicone for a great seal and is easy to clean and sanitize. Tapered design ensures it will fit most oak barrels as well as the hole in most variable volume lids. Top measures 2.5" including flange, 2.25" excluding flange. Tapers to 1.75" diameter at bottom.