17/19/21mm inserts are compatible with Medela, Spectra, Elvie, Willow, TSRETE, Bellababy, Momcozy, and NCVI 24mm breast shields. It reduces the 24mm shielded nipple tunnel to 17/19/21mm. Also works with most other brands of models 24-25mm, including Freemie. It is BPA free, ensuring the highest level of safety for your baby. This accessory helps the breast shield to express more efficiently and maximize milk expression while helping to avoid nipple damage or irritation. This design is an excellent solution for mothers with small nipples using large breast shields, where proper nipple tunnel fit is essential for comfortable and efficient breast milk output. Easy to clean; wash with hot water or on the top rack of the dishwasher. Package includes: 3 breast shields. If you have any questions, concerns, or need further information, please feel free to anytime. Our team is dedicated to providing support and answering any inquiries you may have. Your satisfaction is our ultimate goal. We look forward to offering top-quality products and service. Thank you for your support.