Used on cookers and canners built prior to 1977. Allows excess steam to escape. Fits Presto Pressure Cooker models: 01/PCA4, 01/PCA6, 01/PCC4, 01/PCC4A, 01/PCC4D, 01/PCC4H, 01/PCC6, 01/PCC6A, 01/PCC6AD, 01/PCC6D, 01/PCC6H, 01/PCC6HD, 01/PCD4, 01/PCD4H, 01/PCE4, 01/PCE4A, 01/PCE4H, 01/PCE6, 01/PCE6A, 01/PCE6H, 01/PCS4, 01/PCS6, 02/PCA4, 02/PCA4H, 02/PCA6, 02/PCA6H, 02/PCE6H, 02/PCS4, 02/PCS6, 103, 104, 106, 204, 206, 40 (2 1/2qt), 40 (4-qt), 40 (6-qt), 403, 404, 406, 50, 60 (2 1/2-qt), 60 (4-qt), 603(US), 603(Can), 604, 700 (3-qt), 700 (4-qt), 700 (6-qt), 703, 704, 706, 733, 744, 803B, 804, 804B, 833, A401, A403A, A403AD, A403AT, A409, A410A, A411A, A412A, A413A, A414A, A415A, A416A, A601, A603A, A603AD, A603AT, A607A, A608A, A609A, A610A, A611A, A612A, A613A, A614A, A615A, A616A, A617A, A618A, A619A, A620A, A621A, A622A, A623A, B301A, B301B, B302A, B401A, B401B, B403A, B601A, B602A, B604A, B605A, C301A, C301B, C401A, C401B, C601A, C603A, KE02A, KE02AT, KE03A, KE03AT, PB01A, PB02A, PB05A, PB06A, PB07A, PB08A, PB09A, PB10A, PB11A, S-60, S-66, SC-35 Fits Presto Pressure Canner models: 01/CA16A, 01/CA16H, 01/CA21A, 01/CA21H, 01/CAA12H, 01/CAA20H, 02/CAA12H, 02/CAA16H, 02/CAA20H, 21, 21AV, 21B, 21S, 5, 7, 7AV, 7B, 7S, CA16, CA16H, CA21, CA21H