Mason Bottle Plastic Rings are compatible with any regular mouth mason jar. While Mason Bottle products are compatible with the metal rings that come with mason jars, they started making a more durable plastic version at the request of parents using baby bottles, but they are also great for short-term food storage (but not canning!). Pair with silicone disks for an easy food storage solution. The plastic doesn't come into contact with the contents, but it prevents rust that can be a problem with regular metal rings. Win-win!