I designed and had injection molded this mason jar airlock that is called HOPTOP. It is used to ferment beverages and foods in traditional widemouth mason jars. Here is the kickstarter campaign: <a href="https://www.kickstarter.com/projects/1640002012/hoptop-mason-jar-airlock-brew-and-ferment" target="_blank">https://www.kickstarter.com/projects/1640002012/hoptop-mason-jar-airlock-brew-and-ferment</a>
You can buy it here: <a href="http://www.flatpackfoundry.com/index.php?route=product/category&path=61" target="_blank">http://www.flatpackfoundry.com/index.php?route=product/category&path=61</a>