The air vent/cover lock (located in the cover of your cooker/canner) automatically exhausts air from the pressure cooker/canner as you begin heating the unit, and acts as a visual indication of pressure in the canner.The small gasket must be in place for the air vent/cover lock to seal completely.Fits Presto Pressure Canner models: 01/C13, 01/C17, 01/C22, 01/PE6, 01/PE3, 01/PA6H, 01/PA6, 01/PA4, 178107, 01/CG22, 171001, 171002, 171003, 174001, 0174510, 175001, 175002, 175003, 175004, 175005, 175006, 175107, 01755, 0175510, 177001, 178001, 178002, 178003, 178003, 178004, 178005, 178006.Presto 85407 Interlock Assembly fits Presto Pressure Cooker models: 215102, 215101, 211101, 135004, 135001, 131001, 126105, 126104, 126102, 126101, 125005, 125004, 125002, 125001, 122104, 122102, 122101, 121004, 121002, 121001, 01/PS6, 01/PS4, 01/PA4H