Made of plastic. Most bottles have standard size connectors. Each pack includes 20 connectors in 5 colors: 4 red, 4 blue, 4 yellow, 4 green, and 4 purple. The connectors feature textured stripes on the surface for easier rotation and secure attachment. Reusable and designed for repeated use. A fun and eonal science activity tool for children. Encourages exploration of basic scientific principles involving air and water, and introduces concepts related to physics, motion, and energy. To create a vortex, connect a bottle filled with approximately 2/3 water to an empty bottle using the connector, then shake vigorously 3 to 5 times to observe the spinning vortex effect. Easy to use and ideal for hands-on learning. Great eonal toy for kids. Suitable as a gift for Christmas, birthdays, and other ocns. Total quantity of items: 20. Specifications: Material: Plastic. Length: approx. 4.8 cm (1.88 inches). Outer diameter: approx. 3.2 cm (1.27 inches). Inner diameter: approx. 2.9 cm (1.13 inches). Weight: 20g per piece. Package includes: 20 x Cyclone Tubes in 5 colors.