Supa Airline Tubing 60m (Pack of 1) is a high quality tubing is designed for use in freshwater or in saltwater aquariums. Internal diameter is 4 mm and the external diameter is 6 mm. Use for connecting air pump to all various aquarium accessories such as air operated ornaments and airstones. Compatible with all air pumps and air accessories that run 4mm internal/ 6mm external air line. Made in the UK.