Feature: -Easy and convenient to use -Increase oxygen levels, lower CO2 and raise pH -It is an important instrument to successfully keep aquatic fish for respiration process -Durable, washable and sintered by high temperature, different from other air stones -Creates bubbles in fish tank while attached to an air pump -Creates water currents and dazzling underwater scenes. Description: Material: Mineral stone + Plastic Size: Approx. 40mm x13mm (D*H),80mm x13mm (D*H) Suitable for inner diameter 4mm soft tube Package includes: 1 pcs Air Bubble Stone Note: Transition: 1cm=10mm=0.39inch Please allow 1-3mm error due to manual measurement. pls make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you