Correct fit of a breast flange for pumping breast milk

This drawing shows the proper fit of a flange for pumping breast milk. (The flange is the cone-shaped piece that fits over the breast and connects to the pump.) The nipple should be centered and move easily within the tunnel. If the flange is too small, the nipple will rub against the sides of the tunnel. This can cause pain and even injury to the nipple. If the flange is too large, air can leak out the sides, and milk won't flow as well.