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

• Grommets for 15 25,30 and 60 liter fermenter
• Use with airlock for fermentation
• Perfect for securing airlock during fermentation

“Airlock grommet for airlock on homebrew beer mead wine fermenter Lid, inside hole diameter is 9 mm, out site hole diameter is 12.5 mm. Gd: 12.5 mm ID: 9 mm OD: 16.8 mm gw: 2.75 mm the: 8.4 mm.”