Tube settings

[Faith]

Hello
Thought I'd start a new thread as I'm certain I'll need it!

I'm starting two tube settings (first attempt). One for a 4.6mm faceted stone for which I have appropriate tube and burs now as advised by Dennis and Sarah.

For the other I was hoping to set a weeny cab - 3mm. My idea was to use two bits of tubing in a telescoping fashion for this. I've bought the tube, one piece with external diameter 3mm, one piece with internal diameter 3mm. I know I'll have to measure a stone and buy one exactly the right size.

I thought this was a good plan to make a nice secure seat and also because I like a thicker bezel (the outer tube is 0.5mm thick), but now I'm worried:

Firstly the tubing doesn't telescope - it refuses to fit maybe a light sand will encourage it tho.

Secondly now I'm worried the full width tube will be impossible to push and I should instead have planned to cut a seat in just one bit of tube with an upside down cone burr...

What do folks think? Is my original telescope idea likely to work?

Many thanks as always
Faith