From the product description, check product page for current description, price and availability:

The large 6.5 gallon size of this carboy fermenter is perfect for 5 gallon batches as there is plenty of head space to avoid blow-off during fermentation.

This carboy has a smooth neck which uses standard carboy fermentor hoods.

from MoreBeer… The Fermonster is a brand new fermenter designed specifically for fermentation. MoreBeer! gave product feedback for over 2 years of development and we think they nailed the design. The large lid allows for easy filling and makes hop or oak additions a breeze. The smooth sides are fantastic for sanitization – no ribs or texture to collect yeast or bacteria.  The 6 gallon size is great for most fermentations, and the larger 7 gallon is available for even bigger beers. The punted bottom allows sediment to collect to the sides so that you can siphon liquid from the center.  Because they are made from vigin PET plastic they nearly unbreakable and a lot safer than similar glass carboys. Also notice the conical top which reduces surface area if you plan to store beer or wine long term.

Made from heavy PET plastic, the same material used in 2 L soda bottles, which is nearly impermeable to oxygen penetration.  Due to the thicknes of the material and the overall geometry the Fermonster does not require ribs or dimples for stability.  That results in a super smooth interior surface that reduces yeast and sediment buildup making it the easiest to clean, most sanitary PET carboy on the market.  The huge 4″ opening makes filling a breeze, and cleanup is as easy as wiping down the inside.  Fermonsters are easily moved by hand or consider using our Carboy Carrier for even greater ease of use.

These fermentors are completely air-tight and the lids sealed tight with an O-Ring.  Additional O-Rings and Lids both with and without holes are available for purchase, see our You Might Also Need items below.

Features:

• 4″ wide mouth carboy – easy to clean!
• Food grade PET plastic construction is nearly impermeable to oxygen penetration
• No hard to clean dimples or ribs
• Volume Markers at 5 and 6 Gallons
• Punted bottom
• O-Ring and Lid with one hole is included
• Additional O-Rings and Lids available
• Weight: 1.5 lbs
• Temperature Limit: 140° F
• Height: 19.25 inches
• Diameter: 11.25 inches
• Completely taste and odor free

from MoreBeer… The Fermonster is a brand new fermenter designed specifically for fermentation. MoreBeer! gave product feedback for over 2 years of development and we think they nailed the design. The large lid allows for easy filling and makes hop or oak additions a breeze. The smooth sides are fantastic for sanitization – no ribs or texture to collect yeast or bacteria.  The 6 gallon size is great for most fermentations, and the larger 7 gallon is available for even bigger beers. The punted bottom allows sediment to collect to the sides so that you can siphon liquid from the center.  Because they are made from vigin PET plastic they nearly unbreakable and a lot safer than similar glass carboys. Also notice the conical top which reduces surface area if you plan to store beer or wine long term.

Made from heavy PET plastic, the same material used in 2 L soda bottles, which is nearly impermeable to oxygen penetration.  Due to the thicknes of the material and the overall geometry the Fermonster does not require ribs or dimples for stability.  That results in a super smooth interior surface that reduces yeast and sediment buildup making it the easiest to clean, most sanitary PET carboy on the market.  The huge 4″ opening makes filling a breeze, and cleanup is as easy as wiping down the inside.  Fermonsters are easily moved by hand or consider using our Carboy Carrier for even greater ease of use.

These fermentors are completely air-tight and the lids sealed tight with an O-Ring.  Additional O-Rings and Lids both with and without holes are available for purchase, see our You Might Also Need items below.

Features:

• 4″ wide mouth carboy – easy to clean!
• Food grade PET plastic construction is nearly impermeable to oxygen penetration
• No hard to clean dimples or ribs
• Volume Markers at 5 and 6 Gallons
• Punted bottom
• O-Ring and Lid with one hole is included
• Additional O-Rings and Lids available
• Weight: 1.5 lbs
• Temperature Limit: 140° F
• Height: 19.25 inches
• Diameter: 11.25 inches
• Completely taste and odor free