The surface of the connectors is made of plastic and features ridges for easier gripping and turning. They can be used repeatedly. The standard size fits most bottles and offers a better fit compared to other connectors (size: 1.3 x 1.9 inches). Use a connector to join a bottle filled with about 3/4 water and an empty bottle. Shake the bottles horizontally 4-5 times, and the water will create a swirling vortex. Ideal eonal toy for children, a great gift for Christmas, birthdays, and other holidays. A useful eonal and interactive experiment tool for classroom learning, homeschooling, and scout activities. Helps promote interest in science and learning. Add food coloring or a small amount of soap to the water to create colorful, bubbly effects in the vortex, enhancing the visual experience.