One size does not always fit all, so Medela developed PersonalFit BreastShields in a range of sizes to meet every mom's needs. Lactation professionals agree that proper BreastShield fit is essential for not only comfort, but also for effective milk expression. Authentic Medela spare parts are engineered, tested and approved to work specifically with your Medela breastpump. Non Medela spare parts can vary significantly in design, materials, and workmanship. All of which may affect the performance of your Medela breastpump. Made without BPA safe for mom and baby. All Medela breastmilk bottles and products that come in contact with breastmilk are and always have been made without BPA. 27 mm.