This #7 Stopper with Hole can be used with your 5, 6 and 6.5 gallon glass carboys. It’s made of quality, food-grade rubber that is durable and easy to clean. The hole in the center will provide a nice snug fit for an airlock. To create a solid stopper, simply use a #000 solid stopper (FE400) to plug the hole.
I purchased 10 of these early fall and they stink of rubber. The brand is Fermenthaus. I have tried boiling and soaking in soapy water for weeks an they still stink. May be OK for putting on your gas can but I won't get near wine.
Works like its supposed to with glass carboys. If you have problems with it popping out, no problem! Once it dries it will stay in place. Also, don't go crazy and push it in too far...I pushed one all the way in and had to run down to the LHBS and get another.
I have several sized of these but sometime they don't stay down in the top of a carboy, they squeeze up and they fall out. Make sure you get the right size, i also flame the top of the carboy before putting the yeast in so if its dry that helps too