MoreBeer made this stopper because we could not buy one in this configuration. We use it with our Stopper Thermowell. It features one 3/8" hole and one 1/4" hole. A racking tube or stainless tube can be inserted into the 1/4" hole with the aid of some lubrifilm, forming an airtight seal, and the 3/8" hole fits an airlock. Even after you wedge all this junk into it, it still fits a carboy neck. Expensive because we are not a stopper making company! - We have to freeze require liquid nitrogen .