A number of distributors and manufacturers - including Harold Import Company, Bormioli Rocco Glass Company and Viceroy Rubber & Plastics - sell rubber gaskets for glass jars on Amazon.com. Rubber gaskets create an airtight seal needed for home canning projects.
Rubber gaskets are usually sold in sets of four or six and fit most regular-mouth canning jars. The outside diameter of the average canning jar gasket measures from 3.5 to 3.75 inches depending on the manufacturer, and the inside diameter ranges from 2.75 to 3 inches. Rubber gaskets often come with a safety tab for easy placement and removal. Most rubber gaskets are non-stick, dishwasher safe and reusable.