THIS CARBOY CAP FITS 3, 5, AND 6 GALLON CARBOYS (DOES NOT FIT 6.5 GALLON CARBOYS). IT FITS TIGHTLY AROUND THE CARBOY MOUTH, AND THE TWO OPENINGS ARE CONVENIENT FOR ATTACHING OR INSERTING TUBES, AIRLOCKS, SIPHONS, OR RACKING CANES. CAPS FOR BOTH OPENINGS ARE INCLUDED.