When you write "looks like a nut" in the description of your thing then somebody can come and "make it a nut"... I simply couldn't resist :-)
This thing is a derivative of Beautiful Chunky Bracelet by tinkerbelle which has been modified using the poor man's screw library by aubenc.
To render (it don't works) or compile (it may take a while) you'll need the library provided in http://www.thingiverse.com/thing:8796.
The angle for the thread should be gentle with the arm but still be a perfectly working nut for a bolt with the right dimensions.
I have not printed this, I would love to see it printed by someone.
Printing tip: Don't be in a hurry. Slow down those wild mm/s and the thread will end up with an outstanding look.