I made this because I didn't have any metal rods to make the existing designs on this site, but I did find 2 5/16th bolts on the ground near my desk. The gears keeps them even as the plates move, and also provide a slight gear-up from the knob to the bolts for faster turning. It does not need to be configured in the opposing configuration shown in the image, but it does help with balance if you leave the bolts long. I used a dab of super glue where the bolt heads and nuts attach to the plastic. They fit really well using my badly tuned printer, but ymmv. See the FreeCAD section for making adjustments.

Supplies:

• 2x 5/16 bolts with nuts (or whatever you have if you want to edit the FreeCAD file)
• 2x m3 x ~16mm bolts with nuts (Yay, a mix of metric and imperial)

Printing instructions:

• 1x Main plate
• 1x Second plate
• 1x Main gear (with or without knob, your choice)
• 1x Main gear retainer

For opposing bolts (as pictured):

• 1x Bolt gear
• 1x Nut gear

For same direction bolts:

• 2x Bolt gear

About the FreeCAD file:

It was designed on v0.21.2 requires the FreeCAD gears workbench addon, installable through the addon manager. Everything you should need (and a lot you don't) is defined in the "dims" spreadsheet, so hopefully anyone able to export from FreeCAD should be able to make substantial adjustments. The gears scale automatically with the changes you make, so tooth count etc. can just be changed in the sheet. Everything has been done with the topographical naming bug in mind using offsets from the origin instead of face attachments. Aside from my rancid naming conventions, I'm quite happy with this model.