Find your perfect breast pump flange fit with a wide range of inserts designed for maximum pumping comfort and milk output. When it comes to breast pumps, fit really matters. Proper fit leads to comfort, and comfort leads to more milk output - and fit starts with your flange. Did you know that your nipple size changes from pregnancy throughout your postpartum journey? It even changes before and after nursing or pumping! A close, comfortable fit promotes comfort and milk output .