The Spectra breast shield flange is designed for use with the Spectra S2, S1, Dew 350, 9 Plus, and M1 breast pumps. This wide neck breast shield is also compatible with Spectra wide neck bottles. If double pumping, please buy 2. Spectra Baby is a top leading breast pump company offering moms the latest innovative breast pumps and supplies. We are a team of lactation consultants and pumping mamas that take this journey very seriously. They want to help provide moms all around the world access to a good quality pump to provide breast milk for their babies. How to understand if you are using the correct flange size: Sometimes it can be difficult to know the correct size flange you are ahead of time, unless you’ve used a breast pump before. 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 it’s 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.