Features 1: Provide bottle a tight seal with this snap-on stopper 2: Material of durable butyl rubber, good heat stability. 3: Rubber Bottle Stoppers Self Healing Injection Ports. 4: Designed for a 13mm or 1/2 inch diameter hole opening. 5: Widely used for liquid culture, BRF Jars, Supplemented substrate jars, Grain Masters.