17 or 19 or 21mm inserts are compatible with Medela or Spectra or Elvie or Willow or TSRETE or Bellababy or Momcozy or NCVI 24mm breast shields. It reduces the 24mm shielded nipple tunnel to 17 or 19 or 21mm. Also works with most other brands of models 24-25mm (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 of choice 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 dishwasher top rack. Easy to clean, don't worry about hiding in the pumpPackage: 3 breast shieldsIf you have any questions, concerns, or need further information, please feel free to contact us anytime. Our team is dedicated to providing you with support and answering any inquiries you may have. Your satisfaction is our ultimate goal.We look forward to offering you top-quality products and serviceThank you for your support. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.