Picking the right size flange is important for both your comfort and pumping success. The flange is the part of the pump that is held against your breast. The width of the tunnel is what determines fit. Research indicates that about 1/3 of nursing mothers find pumping more successful and comfortable with a larger than the standard flange.
In general, if your nipple size is approaching the size of a nickel, you probably will do better with a larger than standard size flange. The best way to determine size is by pumping. Your nipple should move freely inside the tunnel without friction. The photo above depicts properly and poorly fitting flanges. Also, pay attention to your comfort. If pumping is uncomfortable even at a low setting, try a larger flange. A poorly fitting flange can decrease the amount of milk you will get and cause pain and swelling of the nipple and areola. If the flange is too large and too much breast tissue is pulled into the pump, swelling can result as well.
Ameda Custom Breast Flanges (see them here) replace the standard 25 mm flange included with most pumps. Each box includes two flanges (one set) and two inserts. Remember your nipple may enlarge temporarily with pumping, so if you are in doubt as to whether you need a custom flange, go ahead and add the next larger size. The Medium and Large sizes are included with the Ameda Purely Yours Ultra. If your nipples are smallish (about the size of a pencil eraser) you may need a smaller flange like the Flexishield Areola Stimulator (see it here)
Each box of custom flanges contains two flanges (a set) with two inserts.
How To Make Breast Pumping Less Painful
If you have a good quality pump and your nipples are not already damaged, painful pumping is likely due to a poorly fitting breast pump flange.