Compatibility guaranteed or your money back. <p> <b>Note About Using Maymom Tubing to Connect to Spectra S1/S2 Main Pump Unit:</b><p> In most cases, you will use your own thick and sticky pump tubing to connect between the main pump unit and the middle barrier (backflow protector). If you want to use Maymom’s tubing to make this connection, use the Quicker Connector to enlarge the tubing hole first before you connect it to the main pump unit. This way, it is easier to make the connection. The inner diameter of Maymom tubing is designed to fit tight with all other connecting parts. Its inner diameter must not be too large. <p> <b>Disclaimer:</b> Maymom is an independent company. Freemie is a trademark of Dao Health. Medela, Freestyle and Pump in style are trademarks of Medela Holding AG. Spectra is a trademark of Uzin Medicare, Korea. Avent is a registered mark of Avent Ltd Co. UK. Maymom is not affiliated with Dao Health, Uzin Medicare, Avent or Medela. Maymom's product is not endorsed by Dao Health, Uzin Medicare, Avent or Medela.