Permit me to present a stylish way to introduce the concept of gear ratios. For every turn the big gear takes, the little one turns twice.
These gears are designed so that one can snap-fit a single .25" neodymium magnet into their centers. They also permit the wearer to casually throw around the word "neodymium" at parties.
If, as I am, you are a belt-and-suspenders sort of hominin, you might affix the magnets in place permanently with a dab of super glue to prevent the accidental necrotizing of the intestines of pets and small children.
A second magnet on the opposite side of one's vestments will hold the gears in place.
I recommend using these magnets and the Space Age adhesive of your choice.
Will not damage clothing and may actually enhance self-esteem.
Also available on Shapeways should you want something a little fancier than plastic.