These lids work for either regular mouth or wide mouth Mason jars. They have a filter for air exchange and a self healing injection port to inoculate your spawn. This lids help to prevent contaminations and work great! I've been using them for years. Just load up your grain, tighten the lid, pressure cook for 2 hours, let cool and inoculate with a spore syringe or liquid culture. Plastic lids are $5 and will last years Metal lids are $3.50 and will last for years but can rust. Happy to give bulk order discounts. Good luck with your grow!