I've used two main holder parts from Tek_3D design.

My_ Screw, Clamp and Nut should lie flat on the table.

Instead of metal rod, just print the rod with 10-20% infill. It is very strong when printed horizontally. The clamp (collar) as seen on first image has very small tolerance and will effectively protect holder from sliding off the rod. But if you need use M6x1 screw. I was trying to print such screw, but it failed, maybe you will be successful? ;)

Use a sandpaper for My_Nut and My_Screw if tolerances are to small.

I am a beginner, but that solution is really working for me. Now i improved my skills about making proper threads for 3D printing. :)