It has a pretty wide taper to fit almost any barrel bung.

It doesn’t require a bung. It fits snuggly in the barrel’s bung hole. If it is not tight it will leak. I think it would perform better if it had a silicone sleeve.

Your bung should be rubber (I prefer the solid bungs). It must have a hole in it. Just get the size bung for your container (barrel or carboy) and buy that size with a hole.

These had been purchased for a standard 59 gallon barrel. We decided that they seal poorly and do not use them anymore. Thank you.

This airlock is meant to be inserted directly into a barrel bung hole that is 1.5-2" in diameter.