What is the tubing size for the Rena Filstar XP Canister Filters

There seems to be some confusion as to the actual tubing size for the filters some places say 21x26 mm and others say 16x21 mm. Which is it?

A: The tubing that comes with every Rena Filstar XP canister filter is the same for the XP1, XP2 and XP3, 5 feet in length per piece. The XP4 has the same tubing as the other filters but the length is 1.5 feet (6.5 feet total per piece) longer per piece. The inner and outer diameter of the tubing is the same for all four filters 16 mm/id(millimeter/inner diameter) x 21 mm/od (millimeter/outer diameter). The closest inner diameter in inches is 5/8 id with an approximate outer diameter of 3/4". You can purchase factory original replacement tubing at Planet Rena Direct.