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, then observe the vortex formed inside. A great educational toy for children, ideal for Christmas, birthdays, and other holidays. It serves as an engaging experiment tool for classroom learning, homeschooling, and scout activities. Helps promote interest in science and learning. Add food coloring or soap to the water to create colorful, bubbly effects during the tornado demonstration for added fun.