Features:1.The authentic Momcozy wearable breast pump 21mm flange insert accessories are only suitable for use with the Momcozy S9 Pro/S12 Pro wearable breast pump. Momcozy Original Parts FSA/HSA eligible. 2.Easy cleaning, wash Momcozy S9 Pro/S12 Pro pump parts after each use with warm soapy water and rinse well. Please use boiling water/steam, with a temperature of around 100°C (212°F). 3.BPA-free, made of food-grade silicone material. All Momcozy pump parts that come in contact with breast milk are BPA-free, giving you peace of mind about your baby's milk. 4.Made for moms, by moms. We've committed our lives to provide the best breast pumps, accessories, education, and customer care that we can, supporting every mother with the beauty of parenthood. Meeting moms pump wherever, without hassle needs. 5.The size of the flange insert is very important for comfortable and efficient pumping. Some moms experience nipple swelling while expressing, so it is advisable to observe the appearance of the nipple during pumping. If your nipple rubs or feels squeezed in the flange channel, it is an unsuitable flange size and you need to replace the right size flange insert.