I recently got a Hayear 180x C mount Lens for soldering work with my ELP camera, but my small scope stand was too short to get focus. So I whipped up a simple 80mm extension that has M16 Female Threaded hole at the top which is 15mm deep and has fine threads at 1mm pitch. I added a 12mm M16 threaded rod to the bottom that same threads and pitch that screws into the base and is secured with a low profile 6mm M16 Nut.

I printed this in PLA+ for the rigidity needed, and suggest similar. I have tweaked the print profile heavily for the best outcome in strength and accuracy. Everything threaded perfectly for me and needed no cleanup, except maybe where the brim was on the tube, but its external to the threads and cosmetic only. 

If you have a similar scope stand with the hole in the base and need some extra height, then this print is for you!

I have provided the FreeCAD projects as well if you wish to change the thread or dimensions as needed to fit your setup. If you do not want to use FreeCAD, I have provided STEP files for each part as well.

The print profile already has both parts on the same plate, and I have modified, at the object level, the settings needed for each part. I have labeled them clearly if you would like to go in and play with settings yourself. 

Enjoy!