I don’t think that 0.3mm is going to make a difference.
Tubing is measured by OUTside diameter, because it is intended for structural use. Pipe is measured by INside diameter, since it transports fluids and how much it can hold is more important. Hence, 1 inch pipe is really 1 3/8 inches in outside diameter. Something to impress your friends with at your next Trivial Pursuit party… 