I would suggest inserting a small bit of sponge rubber -perhaps Dave W can suggest a suitable bit of neoprene!!! -- in any event squashing a bit into the tube between the bar and tube should give enough of an amount of friction to do the job.

Cheers!

Robbie
2021 Plus Four -- Helga
211-WX-1433

"Fettlebodge"--A chief of the PaddyMogs