[ARC5] need the home-made knob conversion info/video

[J Mcvey via ARC5]

I ran out of receiver knobs, so now I have to improvise. Someone here posted a you tube link that described how to use what looked like a compression fitting and some tubing to interface with the spline. I can see how the copper tubing can be expanded, perhaps with a large torx bit, but the shaft is sloppy in the fitting. I guess I'll have to devise a bushing?
I did want to take a look at that video again, since it seemed to work very well .Why re-invent the wheel?