I made (in Blender) these bolts as gadgets to be shared during a meeting.
I gave each printed bolt screwed into a real (commercial) metal nut, perfectly mating each other.
More info here: http://bit.ly/XEztcr
The full video of the speech (in italian) is also here:
The part of the video that shows my Huxley printing two bolts:
Printed in Silver PLA - nice! - from Reprapworld using my ReprapPro Huxley.
UPDATE (2013/08/01): Actually the printed bolts are M10x16. I forgot I reduced the dimension to speed up printing. So I uploaded also the M10x16 file.
UPDATE (2013/05/05): M10 nut added.
UPDATE (2013/05/05): Nut's hexagon dimensions updated (Thanks to Balthazar)