Durceler 19mm inserts 2pcs a Pack to compatible with Medela Spectra Elvie Rainyb S18 S21 S23 Momcozy S9 Pro S10 S12 Pro TSRETE Bellababy NCVI 24 mm breast shields It will reduce the 24mm shield nipple tunnel down to 19mm Also compatible with Freemie 25mm cups to reduce it down to 19mm Also applicable to most other brands of the models for 2425mm Seamless Compatibility For Optimal Milk Expression Suitable for nipple diameter 1618mmafter a pumping session or measure the circumference of nipple base about 4396 5024mm before a pumping session Great solution for smallnippled mothers using large breast shields Proper nipple tunnel fit is essential for comfort and efficient milk output It can be compatible with Spectra and Medela Freestyle Harmony Sonata and SwingMaxi pumps and other brands BPA free made of silicone material Durable clear and comfortable This accessory helps breast shields for more effective pumping and maximized milk expression while helping to avoid nipple trauma or irritation Maintain compatibility with most handsfree bra You can use most handsfree bra cups with they original 2425mm detachable shields having this insert inside During operation you need to squeeze slightly to make the Insert fully fit with the shield to achieve the perfect effect