Might seem trivial, but when a speaker design calls for say a 70mm circular port ?, is it deemed to be ID or OD?
It is interesting? If a drawing shows a hole dimensioned as 70mm, what is the ID as a port tube will have a a thickness?
I order pipes that are 70 mm. It usually says how big holes to make for them to fit.
Sometimes I go to a store that sells pipes. Looking for something that might fit.
If it is a little smaller or a little bigger, I adjust the length myself.
I try with different lengths and listen to the result. Is not always the length that is calculated that I think is best.
Tube will have a a thickness, perhaps 2-3 mm. Doesn't matter.