Yep, the tube is a tad too big, I used some wedges to center the shaft when tacking it in. 25 mm is pretty close to the upright, in the range of 3 mm, but there's no contact. It's about €8 for the tube and postage if under 2 kg, which limits the length to about 90-95 cm or so.

There's something a bit absurd about mailing a piece of steel pipe, don't you think? :)

Actually yes, especially if it is not the exact correct diameter;) . Thank you very much Albert, but I will find a local solution for that:)
Bye.