Due to manual measurements, please allow a difference of 1-2CM.Description: Durable and material keeps your pet fish healthy and safe. This round air stone ball is no harm to pet fish and easy to wash which can be used for a long time. Suitable for aquariums, aquariums, landscaping tanks, turtle tanks, etc. The air stone connect the oxygen pump to provide fine bubbles for your fish. This kind of air stone is also a great gift for any aquarist. Specifications: Color: blue, greyPlease be reminded that due to lighting effects, monitor's brightness / contrast settings etc, there could be some slight differences in the color tone of the pictures and the actual item.