I needed a quick way to turn a threaded rod for a school demonstration. I found Tjhj's excellent scad to generated one but the size was too small. I adjusted the scad to fit over a standard nut that fits a 1/2 inch threaded rod.

Printed on a MakerBot Replicator 2

Standard print
no raft, no support
.15mm layer height

It's pretty tight around the nut, and extends a hair past it. (it's close enough that you can still lock another nut against the one in the Thumb Nut)