According to that link, two different size tubings....1/8" from Regulator to CarbonDoser® V2.0 Box & 1/4" from Box-to-checkvalve-to-Reactor. These sizes are OD sizes. Again, I'd just go to HD or Lowes and get their polyurethane tubing with this OD dimension. If you wish to test first, just buy a foot and see that it fits into the quick-connect fittings.