This carboy cap is specifically made to fit standard 6.5 gallon glass carboys. It is often used to to prime a 3/8 in.  OD racking cane by putting the racking cane through the center of the cap and blowing into the longer side tube. It can also fit airlocks, or be used as a blowoff assembly by attaching some 1/2 in. ID tubing to the center hole. Handy in most any situation!

NOTE: This product used to be a burgundy color, but has been changed to blue!