Gear Bearing
This is a very cool 'print in place' gear bearing designed by emmett. It is a planetary gear with herringbone gears. The only way to produce this is with a 3D printer. It's very cool, the gears can't fall out because of the 45 degree angle of the gear's teeth. The designer emmett has a youtube video which shows you how it works http://youtu.be/ZghwSBiM0sU. This is one of my favorite toy prints, that could have some practical use too.