Fits most standard aquarium heaters, not air / air tubes. Made of plastic and rubber. Perfect for aquariums, fish tanks and any glass surface. The suction cup is 30mm in diameter with a 24mm clip and can hold a 25mm diameter aquarium heater, PVC tubing or a rain bar. Each suction comes with a clip. Keep your aquarium heater firmly in place with these suction clips. Package content: 12 x black heating cups.