One size does not always fit all, so Medela developed PersonalFit breast shields in a range of sizes to meet every breast feeding mother's needs. Lactation professionals agree that proper breast shield fit is essential for not only comfort, but also for effective milk expression. Unique 2-piece system allows mothers to choose breast shield size for maximum personal comfort while pumping. PersonalFit breast shields are available from Medela in 5 different sizes (21 mm, 24 mm, 27 mm, 30 mm, and 36 mm) - sold separately. Choose the correct size for maximum comfort and pumping efficiency - see image provided. Breast shields and connectors can be purchased separately or as part of a replacement parts kit. For complete range, search for Replacement Parts Kit.