Foam Stopper 35-45mm
Breathable foam stoppers will withstand boiling or autoclaving temperatures, making them ideal for use in preparing a yeast starter. The honeycomb structure of the foam stoppers will act is a filter for any airborne bacteria or wild yeast that might enter the flask. That important because a lot of air is sucked into the flask while it is cooling. You can also leave the stoppers on the flask instead of a fermentation lock. Some people use foam stoppers to replace fermentation locks in their carboys, too.
The small foam stoppers are 35-45mm wide and fit our 500 or 1000 ml borosilicate glass flasks, or a glass carboy.
Foam stopper is exactly what it should be.
Fit my 1000ml Erlenmeyer flask perfectly.
Its a foam stopper. It fit the erlenmeyer. End of story.
Actual diameter is 45mm or 1 3/4". My Kimax 5000ml flask has a 42mm opening and this fits perfect. It can of course be squished as small as you want it.