#6.5 Bored Rubber Stopper Bung - Food grade. Center has 3/8" drilled hole for an airlock or blowoff tubing. You may optionally plug the hole with a #000 solid stopper. Top diameter: 1-5/16" Bottom diameter: 1-1/16" . Fits OUR 6.5 gallon GLASS carboy WITH AN AIRLOCK.