It's hard to define what exactly makes the perfect desk toy, because when you're bored even just a paper clip can be entertaining. What's most important is that it gives you an outlet for fidgeting, and this Main Reduction Gear Unit salvaged from a plane's engine and re-branded as a desk toy should fit the bill.
On a plane the part helped to decrease the RPMs of the propeller, but on your desk it spins at a leisurely four RPM, tempting you to stick your fingers in there and feel that rush when they're not crushed. Seriously, it's actually called the Executive Finger Pincher, and the motor will automatically reverse if you don't get your fingers out in time. For $US2950 it's almost a shortcut to a worker's comp claim, but only if you can convince your boss to give you one for Christmas. [MotoArt]