It is well known that using the correct breastshield size is important for your pumping comfort and optimal breast milk production. We include two 25 mm breast shields that will be more comfortable for the majority of breast feeding mothers. Other sizes are available from Maymom for purchase. Our design of valve allows your precious milk to flow easier into the bottle. The tubing set will fit Lactina, Symphony and Pump in Style Advanced sold before July 2006 AS IS. It will NOT fit Pump in Style Advanced sold after July 2006 or PIS sold prior to 2004. Disclaimer: Medela is a registered trademark of Medela, Switzerland. Maymom is not affiliated with Medela nor does Medela endorse the product.