Buon Vino Universal Stopper
Buon Vino stoppers have a longer taper to help produce a better fit and a snug seal, and a lip that prevents them from falling into your container. Includes a 3/8" hole suitable for an airlock.
#6-7 (small) size is recommended for 3-6.5 gallon glass carboys. This size is also referred to as a Universal carboy bung.