This Nipple shield is a Newborn Extra Small, which has a 16mm diameter opening.
Nipple shields are for latch on difficulties or to protect sore nipples. They are made of thin silicone, and worn only when breastfeeding the baby. This shield provides complete coverage of the nipple. They must not be worn between feedings. Only use nipple shields when recommended to you by a professional (lactation consultant or physician).
Available in two other sizes: Medium (24mm) and Small (20mm).