Kathy Mall 4mm (0.157 Inch Inside Diameter) Professional Durable Clear Flexible Airline Tubing for Aquariums Clear PVC 4mm (0.157 Inch Inside Diameter) airline tubing,Extended wear and tear; This standard 4mm (0.157 Inch Inside Diameter) tubing is great Great for all your aquarium airline needs Clear and flexible tubing that resists kinking Safe for fish and good for fresh or salt water environments