6pk Underwater Treasures Bubble Mist Suction Cups attach to standard airline tubing, allowing you to unobtrusively secure your aquarium oxygen system. The cups' lightweight design and flexibility make them easy to install. Clear and reusable, the cups won't obscure your enjoyment of the tank, no matter how you arrange it. The Underwater Treasures Bubble Mist Airline Suction Cups 6-pk includes six suction cups for convenient placement throughout the tank. Multiple anchor points provide a more secure hold and allow for varied tank set-ups. Standard airline tubing measures 3/16" diameter.