This product is made by Maymom to fit spectra’s S1/S2 pumps in addition to spectra 9 and spectra M pumps. It is known that using the correct size of flange (breastshield) in breast pumping is the most important factor in achieving comfort and efficiency. Every mother was created differently. One or two sizes can’t fit all. This is why Maymom develops more than 12 sizes of flanges spanning from 13 mm up to 36 mm to fit the average mothers and those mothers who need special sizes (e.g. 13, 15, 17, 36 mm). Measure your nipple diameter first (do it after a pumping session), and then use the size selector of this listing to choose the size that is 1-2 mm larger than your nipple diameter measured AFTER a pumping session. There are improvements of this flange over the original spectra design – 1. In addition to spectra’s duckbills, you can use Maymom’s valve/membrane system with this Maymom flange. You can also try other brands of duckbills/valve/membrane on this flange. The chances a