These caps fit on juice and water bottles and turn them into sippy cups! No leak or drip valve keeps drinks in until baby wants to drink! Wide mouth caps fit wide mouth bottles (think Tropicana individual sized orange juice and lemonade). The ring adapters can be used with the Red drink cap to fit other bottles. The blue and yellow fit many water bottles (Fuji, Ice Mountain, Kirkland Springs, etc), and the green fit that 'inbetween size' (small Garotarde, Welches, Juicy Juice, etc). Easy to carry with you, keeps drinks from spilling!