The connectors have a plastic surface and strips for easy twisting. They are reusable. Their standard size (3.3 x 4.8 cm) is ideal for most bottles. Use one connector to join a bottle about 3/4 full of water to an empty bottle. Shake the bottle horizontally 4 to 5 times to create a vortex. This is an excellent educational toy for your children, perfect as a Christmas, birthday, or other holiday gift. It's an experimental, educational, and entertaining tool for school classes, homeschooling, and scouting groups. It helps develop children's intelligence and sparks their interest in physics and learning. You can add dye or detergent to the water to give the small vortex different colors and bubbles, making it even more interesting.