Professional series wide mouth stainless steel mason jar lids are engineered for reliable repeated use and lasting durability. Designed to make hundreds of runs through the autoclave or pressure cooker. ProLids offer a combination of unique features, not found anywhere else. Made of 304 Stainless Steel metal to prevent the rusting of standard metal lids. A solid one-piece design and construction makes them simpler to use and clean. Each lid includes a fitted silicone seal that stays in lid when held upside down. They feature a huge 1/2" heavy duty self-healing injection port and a high quality 0.45 PTFE hydrophobic filter sealed with high temp RTV. These industrial strength components mean you will rebuild them less often. Even when you do, replacing an injection port is super easy, because they fit snug and require no sealant or mess. We sell replacement parts for all our lids. PLEASE NOTE: This version is designed specifically for liquid culture cultivation (not grain spawn), because they feature a hydrophobic PTFE filter which can be held upside down and not leak. If you would like lids for grain spawn, which need more fresh air exchange, checkout our other listings.