Fracs are the spherical gears used to make fractal gearing mechanisms, and their complements are the base forms used for their constructions by boolean operations (Intersection) on spheres and rotational combinations of a 1x1 base generated by spheres. Files surnamed Fibonacci are using Boolean operations on a 1x1 base which is generated by the revolved surface using the Fibonacci spiral. Fracs are useful in many types of mechanisms such as robotics , engineering, farming, cycling, toys, machines, and other power bearing and transmission uses.
Along with other numbered fracs, these are used to complete power bearing and transfer mechanisms with proper working arrangements. There is models for the 1x1 all the way up to 21x13 frac.
The 2 inch in the file names is an aproximate diameter of the bounding sphere but most are bigger. It means that the frac forms are generated by boolean operations on a 2 inch base sphere, and it insures that the scaling is the same throughout all the models.
The north and south poles have pivot points which are great for holding, and there are not many ways to hold the asymmetric fracs.
Along with the other creations already uploaded to cults , here are some interesting examples of what you can build with these fracs:
.100 mm step
Power Bearing Technology