This item is a simple top that has a small indent in the top to facilitate stacking one top on another. I home injection molded this part as I have some of my other Thingiverse parts. More info on my injection molding process is available at http://www.scorchworks.com
Although I am providing a STL and Alibre part files I actually hand wrote the G-code for creating the mold. Note that the point on which the top spins is created with spherical features. I created the spherical mold features by plunging centercutting ball nose bits to the appropriate depth. The mold feature for the top handle was created by cutting circles at increasing depth with a tapered ballnose bit (a Dremel bit that I picked up at a home improvement store).
I also engraved text on the top surface linking back to my Thingiverse page. The text was added using g-code generated by F-Engrave.