Gravity Screw
thingiverse
This STL file comprises a bolt and nut pair that slide on screw threads via gravity alone. A video demonstration can be found at https://www.youtube.com/watch?v=o7VBwFYEDuU. For separate files, consider http://www.thingiverse.com/thing:198940. The file was initially created to test minimal thread size on a 3D printer but proved entertaining, even prompting the creator's wife to bring it to her preschool. The children adored it. If printed at half scale, the model offers a keychain option. Alternatively, visit http://www.thingiverse.com/thing:198940 for separate STL files.
With this file you will be able to print Gravity Screw with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Gravity Screw.