The Bubbler style airlock is the preferred lock for secondary fermenters, as it is possible to monitor the pressure in the fermenter. Includes universal stopper. The universal carboy bungs have a generous taper, so they fit standard 3, 5, 6 and 6.5 gallon carboys. It is impossible to push carboy bungs into a carboy. Unlike stoppers, carboy bungs will seal a carboy when they are still wet.