I came across a prevailing torque nut at the parts store yesterday and thought the name of it was interesting, but no time to look into it. Of course I had no idea it was related my question when posted here... but what do you know...
The bolt in my picture at the beginning of this thread is a -
Prevailing Torque Type Fastener - you can read about them about 1/4 of the way down the page
HERE.
In brief...
Material additive fasteners work by wedging the fastener into close proximity with the mating thread, causing a metal-to-metal drag in the circumferential direction directly opposite to the material locking device. The material used to produce the wedge customarily is an engineered plastic.