I got these to try to switch my baby to playtex nursers, since he started taking the lids off his regular bottles (chicco duo). Since I can twist the lid a lot tighter on the nurser, he is unable to loosen the lid and dump his milk on the carpet. The medium flow nipple wasn't to his liking so I ordered these. They drip pretty good when tilted over, so I'm sure he's getting a good enough flow, but he needs some time still to get used to the bottle switch. The nipples fit perfectly, just push the old one out and the new one in.