Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5410576.
This is basically a tool/work piece holder with a spring and nut-bolt system that will give maximum pressure. Ease of use is compensated with the pressure and holding lock provided with the bolt. For reference on how to assemble please see the images. You can use upto 5mm diameter bolt but I prefer 3mm bolt with 30mm length. Nut should be having outer diameter less than 7mm and thickness 3mm.
This is a multiuse design. I made it with the intention of using it as a holder while soldering PCBs. I have also attached solidedge files of this so that you can also edit it to fit your requirements.
There is no need to give supports. Also advisable infill is 20%.
If you find that your nut is lose inside the cut out please glue it in the correct spot with some high bond glue or glue gun.