If you are looking to impress you can make a cool Planetary Gear Business Card. If that isn’t for you then have a look at this circuit board business card or this metal business card that belongs to the Woz."Cut from card or bristol and assemble like a sandwich. The middle layer needs to be appreciably thicker than the others; I cut it twice and glued the bits together, but I recommend using thicker paper board. To keep the planetary teeth gears from getting caught up in the window edges, bend the gear teeth down (towards the back layer) slightly before assembly. Glue down the middle (sun) gear only. You can put three or four planetary gears inside. It’s a bit tricky to assemble; a spare pair of hands helps."