The Spectra flange is designed for use with the Spectra S1 Plus, Spectra S2 Plus, Spectra Dew 350, Spectra 9 Plus, and M1 breast pumps. This wide neck breast flange is compatible with Spectra bottles that have a wide neck. Sometimes it can be difficult to know which size flange you are. Your flange size has nothing to do with your breast size. The size of your nipples will determine your flange size. Some moms will experience nipple swelling while pumping, so its important to observe how your nipples look during a pumping session. The size of your flange is important for comfort and efficient pumping. While pumping, your nipple should not rub or feel squished inside the flange tunnel. All of your nipple should fit into the flange tunnel and move in and out freely. If you feel any discomfort or nipple pain or nipple blanching (turning white) while pumping, you may need a larger flange. Some moms may need a different flange size on each breast, and this can change over time. To determine your flange size, please see a lactation consultant. Owned and operated by fellow moms, lactation consultants and registered nurses, Spectra is committed to supporting every mother on the beautiful journey of breastfeeding. From our unique Natural Nursing Technology to our one-of-a-kind customer care, you can count on Spectra to be right there with you, every step of the way. We are moms. We are nurses. We understand.