Add to your stock of homebrew supplies with this drilled rubber stopper. Made of solid rubber with a drilled hole that's perfectly sized for an airlock, this plug is perfect for keeping oxygen away from your fragile fermentation. Just pop this #6 drilled rubber stopper into the mouth of your carboy or fermenter, insert an airlock, and let nature do the work! *please note: for best results, measure the diameter of the mouth of your carboy or fermenter and Compare to rubber stopper measurements to find a good fit. *. in stock and ready to ship. Features: made of rubber. Creates an Airtight seal in the mouth of your carboy or fermenter. specs: dimensions: 1 1/16' bottom diameter; 1 1/8' top diameter. 1 x #6 rubber stopper airlock hole, country of origin - Canada, manufacturer name - Brewcraft.