17/19/21mm inserts are compatible with Medela, Spectra, Elvie, Willow, TSRETE, Bellababy, Momcozy, and NCVI 24mm breast shields. They reduce the 24mm shielded nipple tunnel to 17/19/21mm. Also compatible with most other brands featuring 24-25mm models, including Freemie. Made from BPA-free materials to ensure safety for your baby. This accessory helps improve breast pump efficiency and maximize milk expression while helping to prevent nipple discomfort or irritation. Designed for mothers with smaller nipples using larger breast shields, where proper nipple tunnel fit is essential for comfortable and effective milk expression. Easy to clean—wash with warm water or place on the top rack of the dishwasher. Package includes 3 breast shield inserts.