Medela Breast Pump Membranes, For PersonalFit Flex, Replacement Piece, Yellow, 101044540, Pack of 2 are spare or replacement membranes for your PersonalFit Flex Connectors, which are included with Medela’s Freestyle Flex, Swing Maxi, Pump In Style with MaxFlow, and Solo Breast Pumps. Medela recommends replacing your membranes every 3 – 6 months, depending on your pumping frequency. Replace immediately if you notice damage or extensive wear. IMPORTANT: Use of pump parts or accessories not designed for your specific breast pump may cause irreversible damage to the product. For that reason, only use the accessories that came with, or are identified by Medela to work with, your specific breast pump model. Each pack contains two (2) silicone membranes.