My cheap digital microscope has a diameter of 35mm and the stand is very wobbly.

what you need :

1. 18 mm tubing/steel rod (my choice : 18mm copper tubes(out of my collection:-))
2. M6 nut(s)
3. M6x45mm hex screw(s)
4. knobs
   (taken from : Parameterized Star Knob for tool by Hank-Cowdog
   https://www.thingiverse.com/thing:664192 )

(photos will follow)