maymom breast pump accessories for medela pump in style pumps, mm large breastshields (27 mm (large)) maymom it is well known that using the correct breastshield size is important for your pumping comfort and optimal milk supply. it is also known that one-piece design offers easy to clean, fewer pieces to keep, and no seams to lose suction power. <p>maymom is the first company world-wide to offer 15, 17, 19, 21, 25, 26, 27, 29, 30, 34 and 36 mm internal diameter one-piece design breastshields to fit medela users personal pumping needs. the valve/membrane in this set are interchangeable with your existing medela parts. maymom has 4 years experience in making breast pump parts. 100% compatibility is guaranteed or your money back! <p><b>disclaimer:</b> medela and pump names (pump in style, swing, freestyle etc) are registered trademarks of medela holding ag. maymom is not affiliated with medela nor does medela endorse the product.</p>