17/19/21mm inserts are compatible with Medela/Spectra/Elvie/Willow/TSRETE/Bellababy/Momcozy/NCVI 24mm breast shields. It reduces the 24mm breast shield's nipple tunnel to 17/19/21mm. Also works with most other brands of 24-25mm models (Freemie). It is BPA-free, ensuring the highest level of safety for your baby. This accessory helps the breast shield pump more efficiently and maximize milk expression while helping to avoid damage or irritation to the nipples. This design is an excellent solution for mothers with small nipples who use large breast shields, where proper fit in the nipple tunnel is crucial for comfortable and effective breast milk production. Easy to clean, wash with warm water or in the top rack of the dishwasher. Easy to clean, don't worry about it hiding in the pump. Package: 3 breast shields. If you have any questions, concerns, or need further information, please do not hesitate to contact us at any time. Our team is dedicated to providing you with support and answering any questions you may have. Your satisfaction is our ultimate goal. We look forward to offering you products and services of the highest quality. Thank you for your support.