We've been there and hence this nursing essentials gift set. Tested to ensure zero Chemical leaching, no BPA, leads, or Phthalates. Made up of 2 inserts. This product has a variety of models, which can change the size of the "breast milk channel" on the cover of the breast pump, so as to be suitable for mothers with different nipple sizes, help to improve the breast feeding efficiency and increase the pumping capacity, and make mothers more comfortable in the process of breast feeding.EASY TO CLEAN: Boiling water safe, Steam safe, Dishwasher toprack safe. Food-safe, seamless design. Second Generation Improved Flange Inserts: two levels taper design for milk flow without blocking, do not reduce the suction of the original pump. BPA and DEHP Free. SAME SUCTION AS ORIGINAL PUMP PARTS. EASY TO INSTALL REMOVE. AVAILABLE IN 15, 16, 17, 18, 19, 20, 21mm. 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: Elvie Elvie Stride pump 24mm, Willow Gen 3 pump 24mm, Momcoyz S9 S10 Pro S12 Pro M5 Wearable pump 24mm, Lansinohh pump 25mm, Freemie pump 25mm, for Spectra S1 S2 pump 24mm, Medelaa pump 24mm, Amedaa MYA pump 24mm, Philip AVENTT 25mm, Maymom 24mm, Evenflo pump 24.5mm, Dr. Brown's pump 25mm, TSRETE Wearable pump 24mm, FEISIKE Wearable pump 24mm, Rainyb Wearable pump 24mm. It will reduce the 24-25mm breast shields nipple tunnel down to 16mm. 2pcs each pack.