One-piece construction for easy cleaning. Can be sanitized with water steam, boiling water or microwave-steam bags. 2*18mm flange are compatible with the Spectra S1/S2,S1/S2 PLUS,9 PLUS. 2*duckbill valves Not original Spectra Pump Parts. Available in multiple sizes: 15mm,16mm,17mm,18mm, 20mm, 21mm, 22mm, 24mm, 26mm, 28mm. Please refer to the size selection guide in the product subpicture,if you don't know how to choose your size. If you have any questions,please feel free to contact us and we will answer you within 24 hours. MOOMentaneous 18mm Flange and Duckbill