This spout is a direct replacement to the spout already on the nuk first choice learner bottle its always handy to have a few spouts around due to the amount of times you may wash the original spout and also the spout may be damaged by the baby chewing on the teat you could also rotate the use of the spout to increase the life of one made from tpe a soft yet tough material that cannot be bitten through aiding the transition from silicone teat free flow spout gets babies used to