The tapered fit means that you can use this stopper in a variety of sizes of carboys, and still get a secure fit.

This Universal Stopper fits a variety of carboy neck sizes and even most 500ml Erlenmeyer flasks! Try it in a 3, 5, 6, or 6.5 gallon glass carboy. (DOES NOT FIT BETTER BOTTLE OR PLASTIC CARBOYS.) The longer taper is made from a different material that doesn't pop out of your carboy when it gets wet. It is our stopper of choice for all applications involving these size carboys. This is the solid version of FE494 (universal stopper with hole).