Ameda Custom Fit Flanges With InsertsAmeda Custom fit Flanges with Inserts (XXL XL) The Ameda Custom Fit 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. If pumping causes discomfort,