That is something that I have got custom to here as I deal the various effects of Ethanol and other fuel additives. The line shrinkage is something that has to taken into account with replacing lines especially on those tank through holes. Many of the lines that I replace that has already been replaced are usually because the installer went for only a slightly fiction fit.
As Aussietrev mention you do need taken account both the ID and OD sizes and many aftermarket lines will fit one way but not the other on some setups. I especially had problems with Homelite trimmers here until I found some aftermarket Echo rubber fuel lines that had the ID and OD that I was needing.
Also when installing new lines it is better to pull the lines through than trying push them. This way you take advantage of fact that these lines OD when stretched shrink temporarily allowing them to slipped through easier. When pushing the opposite is happening which makes them even harder to get through.
To me there is no hard and fast rule here as you need some experience with the conditions on your end which lines works best on which products. It has took me several years of trying different lines to settle on which works best for which products and then the manufactures will change things just makes things different.
Patience is key to working on these.
