This is a functional differential gear system. For those unfamiliar, a differential allows two output shafts to be spun at different speeds from a single input shaft. You will find these in most cars on the road. For more info see http://auto.howstuffworks.com/differential1.htm Updated: Differential2.zip file includes the SolidWorks source files and a DXF of the print. Created with the aid of this document: http://ewp.rpi.edu/hartford/users/papers/engr/ernesto/brownm2/EP/Final%20Report/Design%20and%20Analysis%20of%20a%20Spiral%20Bevel%20Gear.pdf1)Print 2)Assemble Casing 3)Attach Input Pinion to Stand 4)Attach Casing to Stand