Tubing and pipe is always O.D. , outside diameter.
No.
Tubing is measured by OD, so the fluid path is smaller depending on the wall thickness of the tube. PIpe is measured by ID. Thus a "1/2 inch" pipe is huge compared to "1/2 inch" tubing. 1/2" tubing would be a tight fit INSIDE 1/2" pipe. Of course, most pipe is not precision-made, so the actual fluid path varies somewhat.
Hose whether rubber, Teflon, buna, synthetic, is always measured by I.D. inside diameter.
Not exactly. Hose can be measured by ID in some cases. In other cases the ID is similar to a same-nominal-size tube. In other words, the nominal size minus the wall thickness of the tubing. The actual ID is smaller than the nominal ID.
Examples:
Aeroquip 2807 "Teflon" / "PTFE" steel-braided hose, -4. Nominal 4/16 = 1/4" hose. Actual inside diameter .19 rather than .25. Similar to 1/4" tubing with a .030 wall thickness.
2807 -8 Nominal 8/16 = 1/2" hose. Actual inside diameter .42 rather than .50. Similar to 1/2" tubing with .040 wall thickness.
Aeroquip FC300 -8 reinforced rubber hose with polyester outer braid. Nominal 8/16 = 1/2" hose. Actual ID is .41 rather than .50. Similar to 1/2" tubing with .045 wall thickness.
NAPA NBH H178 "3/8 inch" fuel hose, nominal 3/8", actual ID is .375 = 3/8 inch.