Maintain compatibility with most handsfree bra. You can use most handsfree bra cups with they original 24 25mm 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. 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. AVAILABLE IN 15, 16, 17, 18, 19, 20, 21, 22mm. MADE FROM SOFT SILICONE: Soft silicone makes pumping more comfortable, and suitable for moms with smaller nipples. Correct flange sizes make pumping more efficient. Seamless Compatibility For Optimal Milk Expression: Suitable for nipple diameter 12-13mm(BEFORE a pumping session), or measure the circumference of nipple base about 37.68-40.82mm(BEFORE a pumping session). COMPATIBLE PUMPS: Durceler 2 Piece 16mm Flange Inserts for Spectra S1 S2, Medeal Pump in Style with MaxFlow, Manual Harmony, Swing, Freestyle Flex, Swing Maxi Electric, Symphony, Lactina, Sonata, Momcoyz S9 Pro S10 S12 Pro, Bellabayb, Willow Hands-Free breast pump wearable 24mm Cups Shields. Also compatible with Lansinho, Lansinho SignaturePro double electric breast Pump, Freemie 25mm Cups Shields. It will reduce the 24-25mm breast shields nipple tunnel down to 16mm. 2 pcs each pack.