It's made of plastic. Most bottles have normal size connectors. Each bag has 20 connectors in 5 colors, of which 4 are red, 4 are blue, 4 are yellow, 4 are green and 4 are purple.The surface of connectors has stripes, thus much easier for you to rotate, can be applied repeatedlyIt is a great educational and fun experiment activity toolGood for kids to explore some of the scientific properties of air and water, and to stimulate their interest to physics, dynamics and potential energy.Use a connector to connect a bottle with about 2/3 of water and an empty bottle, and shake it vigorously for three to five time, then you will see that the vortex in the bottle is rotatingThe tornado you expect is formed, so easy.It's great educational toy for your kids, perfect gift for Christmas, Birthday, and the other holiday.The number of the following items should be 20.Specifications:Material: PlasticLength: approx. 4.8 cm/ 1.88 inchesOuter diameter: approx. 3.2 cm/ 1.27 inchesInner diameter: approx. 2.9 cm/ 1.13 inchesWeight:Each 20gPackage includes: 20 x Cyclone Tube in 5 colors