those numbers are correct. look
here. scroll down until you see the hose clamps; its says:
"19/32"-21/32" is for our 3/8" Hose
11/16"-13/16" is for our 1/2" Hose"
5/8 OD (20/32) tubing fits the 19-21/32 clamps, amd 3/4 OD (12/16) tubing fits between the 11-13/16 clamps.
also look at the
DD instructions page. it says
"...Feet of 3/8” Inner Diameter Hose (5/8” OD Recommended)"
so yup, those are correct #'s. i guess the think wall will help prevent the hose from kinking when making tight turns (makes sense yes?)