A stopper that fits a 2.8, 3, 5, 6, or 6.5 gallon glass carboy(does not fit better bottle or plastic carboys). also fits a 500 ml Erlenmeyer flask. Made with a longer taper from a different Material, this stopper does not pop out when wet. Much more reliable, it is the stopper of choice for all applications involving these Size carboys. Also will fit a 12 or 22 oz. beer bottle when used upside down.