This is the replacement gasket that seals the lid onto the body of the plastic Speidel fermenters. This gasket generally does not wear down through normal use and need to be replaced. That being said, everyone seems to manage to find creative ways to use our equipment that results in needing replacement parts!This gasket fits our 20L (5.3 gal) & 30L (7.9 gal) Speidel Plastic Fermenters.