Homebrew Fermenter Bungs, Grommets & Airlock Seals

How do I choose the right bung or grommet for my fermenter?

Measure the opening first, then match it to the size range in the product name. The 28-30mm bored bung fits a 5L flip-top glass demijohn and is not compatible with wide-mouth screw-top demijohns, which need a wide-mouth stopper in the 38-46mm range. The 28-32mm solid bung fits 23L glass carboys and 5L flip-top demijohns when you do not need an airlock hole. The 19-26mm red rubber bored bung is compatible with the Mangrove Jack's stainless steel fermenter. For a plastic fermenter lid that already has an airlock hole, the black grommet suits it and works with both Senior and Vintage airlocks, and its centre groove clips it into the lid so it resists being pushed out if pressure builds during fermentation.