The minimum size of tubing for the supply line is ____-inch (9.5 mm) od tubing.

The minimum size of tubing for the supply line being identified as 3/8-inch (9.5 mm) od tubing is consistent with guidelines that aim to provide adequate flow rates while preventing excessive pressure drops in the piping system. This size strikes a balance between sufficient volume delivery and manageable material costs, making it a common standard in various installations. Smaller tubing, such as 1/4-inch or 3/8-inch, may not provide the necessary flow for many applications, while larger sizes, like 1/2-inch or 5/8-inch, might not be justifiable due to increased materials and potential cost concerns without significant advantage in flow capability. Thus, 3/8-inch serves effectively as a minimum requirement for a reliable supply line under typical circumstances.