For heaters and fluorescent tubes: Diameter: 3.2 cm for the clips and 3.2 cm for the suction cups. Perfect for holding aquarium heaters and submersible or external fluorescent tubes. Not suitable for hanging tubes! POWERFUL SUCTION CUP: The suction cups are made of soft, flexible rubber and adhere firmly to your aquarium or any other glass surface without coming loose. STURDY PLASTIC CLIPS: Each suction cup comes with a large, robust plastic clip. Securely attach your aquarium heater or fluorescent tube to keep it in place. Detachable design: Align the clip's groove with the suction cup's protrusion. Insert the clip into the groove and rotate it 90 degrees to lock it. Then, turn the clip and remove it from the suction cup's base. EASY MAINTENANCE: Simply clean and dry the suction cups and the glass surface before installation. Replace them if they are worn after prolonged use.