Size 1: this is also known as a newborn flow but these nipples are designed with a standard side hole so it suits with babies who are from newborns to one month old. (shrewdmommy.com)
It's just a bit harder to wear because of the ol' side holes. (cici-marie.com)
It is silk lined and has two side holes for easy mobility. (inhonorofdesign.com)