From the message "Friday Challenge" in alt.machines.cnc and rec.crafts.metalworking

This is a few rendered pictures of a part I (somehow) had to grind on the "tail" part.

  The "pigtail" is a core for a mold, forming a hollow inside the finished
part.

  The pigtail is bolted on the flange of the spindle, and runs inside a large
multi-thread bronze nut.  When the core is drawn back from the mold, the threads
provide the necessary rotating motion to unscrew the core