"Shield size" refers to the physical dimensions or measurements of a shield, usually its width and height, which determine how much area it can cover and protect. Full definition
If you feel discomfort while pumping or still feel full after a pumping session, it may be a sign you need to change your breast shield size for one or both breasts. (talesofamessymom.com)
Luckily, we have included three different shield sizes in the box so you can mix and match to find what works for you. (pumpables.co)
The most common reason for pain when pumping is using the wrong shield size, so make sure you find the right one. (pumpables.co)