Supa Airline Straight Connector Twin Pack are the easiest to allow airline tubing to be joined together. Made from quality materials that are non-toxic & odourless. Designed to fit airline tubing with an internal diameter of 4mm and an external diameter of 6mm. Part of an extensive range of airline accessories from Supa Ltd Supa have been involved the aquatic trade since 1949, so have built up over many years a vast knowledge & experience of all that is essential for successful fish keeping.