The Maymom 21mm Flange and Duckbill Valve set includes two flanges and two duckbill valves designed for compatibility with Spectra S1, S2, and Spectra 9 Plus breast pumps. These parts are not original Spectra components but are engineered to perform with the same suction power as OEM parts. The flanges are made from BPA/DEHP-free materials and are FDA compliant for food contact, ensuring safety and durability. They can be used with various wide-neck bottles, including Spectra and Maymom bottles. The duckbill valves are designed for easy installation and removal, providing a reliable and efficient pumping experience.