Buon Vino stoppers have a longer taper to help produce a better fit and a snug seal, and a lip which prevents them from falling into your container. Available with a 3/8 inch hole for an airlock, or solid with no hole.
#6-7 (small) size is recommended for 3-6.5 gallon glass carboys. This size is also referred to as a Universal carboy bung.
Universal Stopper, Small, Solid
$1.49