The Ameda CustomFit Breast Pump Flange Kit helps make breast pumping comfortable and helps mom pump more milk when the fit is just right. The breast flange is the funnel shaped piece that cups your breast. A good fit is important! Make sure your breast flange is not too small or too large. Using the wrong size will cause discomfort and reduce the effectiveness of your pump. The Large/Medium CustomFit Flanges provide moms with larger breast flanges and special reducing inserts to create a smaller size for maximum pumping effectiveness. If pumping causes discomfort, even on a low suction setting, you may need a different breast flange size. All Ameda HygieniKit Milk Collection Systems come with a standard size 25.0mm flange that works well for many moms, but we also offer a range of different flange sizes and inserts – our CustomFit Flange System – to ensure you find your best fit.