5Pcs 2/2.5/3/4/5cm Aquarium Air Bubble Stone Fish Tank Oxygen Aerator Pump Ball. Specifications: This ball helps increase oxygen levels and lower CO2. It is an important instrument to successfully keep fish for respiration process. The stone is durable, washable and sintered by high temperature, different from other air stones. Creates bubbles in fish tank while attached to an air pump. Item Name: Air Bubble Stone Material: Sand Stone, Plastic Features: Washable, Reusable, Easy to Use S Size: 2cm x 2cm x 3.3cm/0.8" x 0.8" x 1.3", Nozzle Diameter: 0.4cm/0.16" (Approx.) M Size: 2.5cm x 2.5cm x 3.8cm/1" x 1" x 1.5", Nozzle Diameter: 0.4cm/0.16" (Approx.) L Size: 3cm x 3cm x 4.4cm/1.2" x 1.2" x 1.7", Nozzle Diameter: 0.4cm/0.16" (Approx.) XL Size: 4cm x 4cm x 6.6cm/1.6" x 1.6" x 2.6", Nozzle Diameter: 0.4cm - 0.6cm/0.16" - 0.24" (Approx.) 2XL Size: 5cm x 5cm x 7.6cm/2" x 2" x 3", Nozzle Diameter: 0.4cm - 0.6cm/0.16" - 0.24" (Approx.) Notes: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Package Includes: 5 x Air Bubble Stone