Stage 1 is slow flow rate nipple while stage 2 is medium flow rate. (babieslounge.com)
This way you can use this bottle with four week old babies that require very slow flow rates as well as with older ones that demand faster supply of milk. (babygearhub.net)
This pack comes with the 4 ounces baby bottle with two different nipples, one for slow flow rate and one for medium flow rate. (babieslounge.com)