Summary

Those designs are different types of nozzles and a cork for seal guns.
You can chose nozzle sizes between 2 and 5 mm. I like the 2mm for delicate works.
All models can be printed without support and need no post treatment.
For a smooth result use 0.4 layer thickness. The walls are designed to be to layers thick.

Edit: After being asked in comment i added 2 models with 1mm holes: "1mm.STL" and "1mm_thin_walls.STL". The first one uses the exact same design with 0.8mm walls but it seemed like a precise work requiring 1mm holes would be wasted by 1.6mm of plastic. So the second model "thin walls" uses 0.4 mm walls. High pressure might break it so bee cautious and don't hesitate to give feedback on those models.