Abstract: A nipple adapter in the form of a unitary assembly for receiving the external thread of a bottle with a narrow neck is disclosed. The nipple adapter may be fitted to commercially available bottles and containers having a wide variety of beverage contents such as water, mineral water, juice, milk and soda pop. The nipple adapter has a cover, a nipple with a flange, a seal and a housing. The cover has an inner shelf extending circumferentially around an interior face of the cover. The inner shelf has an inner land and a negative angular portion extending from the inner land to the interior face of the side wall of the cover defining a triangular cross section. The housing has an outer shelf disposed on and extending circumferentially around an outer annular wall. The outer shelf has an outer land extending from the outer annular wall and a positive angular portion extending from the outer land to the outer annular wall defining a triangular cross section.