#8.5 Rubber Stopper with Airlock Hole - High-Quality Silicone/RubberThe #8. 5 Rubber Stopper with Hole is a professional grade closure designed for 5 and 6 gallon glass carboys. Made from high quality, food grade rubber, it provides a 100% airtight and liquid tight seal. This model features a pre drilled center hole, specifically sized to accommodate standard twin bubble or 3 piece airlocks. Its tapered design ensures a snug fit across the neck of most standard homebrew carboys, protecting your beverage from oxygen