The surface of the connectors is made of plastic and has strips that are much easier for you to turn. They can be applied repeatedly. The usual size for most bottles is better than other connectors (size: 1.3 x 1.9 inches) Use a connector to connect a bottle with about 3/4 water and an empty bottle. Shake the bottle horizontally 4-5 times, then the swivel in the bottle rotates Great educational toy for your children, perfect gift for Christmas, birthday and other holidays It is a great educational and entertaining experiment tool for school classes, home schoolers and scouts. It can help to increase children's intelligence and awaken children's interest in physics and study You can add colour or washing powder to the water in the bottle so that the small tornado you create has different colours and bubbles, which is more interesting