I do most of my assembly under a microscope, so I like the holder to be as low profile as possible. A good friend made me a wooden one years ago, so I adapted it to the 3D printing world.
The picture is of the prototype. I doubled the guide rods to allow for bigger PC boards in the published STL file. My friend used a bolt, nut and a spring to hold the plates together, so I incorporated the holes needed in the design, but a rubber band will work in a pinch. I had a 1/4-20 bolt, but not a good spring, so rubber band it was.
The hole was the right size for the guide rods except where the first layers were. I reamed it out with one of the metric hole drills in the picture attached. They work in steel, but even better in Thermoplastics.