I discovered a very nice OpenSCAD library called “Nut Job” http://www.thingiverse.com/thing:193647 that was quite inspiring, it looked like a nice test for the printer. I first tried a 8mm nut and a bolt, and the result was just great on first attempt:
I had to try some more, model on the left, print result on the right…
A quick check confirmed they all fit together and will work fine for a lot of purposes. Even the countersunk screw could be used with a hex spanner. It was tight, but that is probably a good idea anyway. What didn’t work was threading a metal nut onto the printed screws, the thread pitch was different. It can be adjusted in the ‘Nut Job’ library, so perhaps the print can be done compatible with metal screws/nuts. However, that is probably not usually required as the nuts and bolts are printed together.
This could be used in many ways of course. As shown or as embedded threads in prints so that parts can be screwed together.