Trust Dr. Brown’s baby feeding system to keep your little one nourished and happy with minimal feeding problems. These silicone nipples are designed for Wide Neck Natural Flow Baby Bottles, both 4oz and 8oz sizes. Level 1 teats are perfect for babies from birth and up. Level 2 teats are perfect for babies from age 3 mo. and up. Level 3 teats are perfect for babies from ages 6 mo. and up. Level 4 teats are perfect for babies from ages 9 mo. and up. Y-cut teats are perfect for thicker liquids.