A great carboy hood for a real snug fit. Fits our 3, 5, and 6 gallon glass carboys. Will also fit over our 5 and 6 gallon plastic carboys.Ideal to use if you have a real active fermentation. Add 3' of 1/2" racking tubing to your 3-piece airlock. Take out the bubbler piece to assemble into a blow-off setup.