Contains 2x 27mm widemouth flanges for spectra s1 pump, s2 pump and 9 pump. Suitable for mother with a nipple diameter 24-26 mm (measured AFTER a pumping session). Suitable for spectra s2 accessory replacement. They are NOT compatible with OTHER wide mouth bottles. Made by Maymom, not original spectra company. Maymom is not affiliated with Uzinmedicare, the trademark owner of spectra. Dishwasher toprack safe; Steam safe sterilization; Maymom provides great alternatives to speCtra pump parts for spectra S2 accessories and spectra S1 accessories. This product is made by Maymom to fit speCtra S1/S2 pumps in addition to speCtra 9 Plus and speCtra M pumps. It is known that using the correct size of flange (breastshield) is the most important factor in achieving comfort and efficiency during breast pumping. 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 in need of special sizes (e.g. 13, 15, 17, 36 mm). Measure your nipple diameter first (do it AFTER a pumping session). Then, refer to the size selection guide of this listing to choose the size that could fit you. Unique compatibility features of this flange – Duckbill Valve Systems - Maymom flanges can adapt to spectra's duckbill valves and Medela or Maymom's valve/membrane system. Backflow Protector Systems - This Maymom flange can adapt to Maymom's long or short stem backflow protector in addition to speCtra's backflow protector. . Pump Systems - With a tubing connector (sold separately) or original Medela tubing, this Maymom flange can also be used with Medela pump in style, Symphony and Lactina pumps. This feature enables users to use their Medela pumps with wide mouth bottles without an extra bottle adapter.