uxcell Mineral Aquarium Fish Tank 4.5mm Outlet Encased Bubble Air Stone 20" Green Blue Can easily driven by even Nano air pumps, suitable for aquarium, fish tank and circulation system. Air Stone Body Length : 50cm/ 20" Total Size(Approx.) : 53 x 2cm / 21" x 0.8"(L*W) Hole Outer Diameter : 4.5mm/ 0.18" It is an important instrument to successfully keep aquatic fish for respiration process