21 mm insert for the My Hands Free Electronic Breast pump Cups.
Flange size is important for effective breast draining and comfort.
How to measure the correct flange size:
Measure the diameter of your nipple. Only the part that sticks out not the areola (darker pigmentation around the nipple).
Once you have this measurement add 5/6 mm to find your correct flange size.
Nipple measurement of 16mm + 5mm = 21mm