Doug White wrote:
... a thin, soft washer under the nut. Once everything is tight,
they pry up one edge of the washer against a flat on the nut. ...
The nut can't unscrew because of the tab folded up against it, and the
washer can't come loose if the nut doesn't. ...

Well, the washer & nut can turn together, unless the washer is keyed to
the shaft (I have stuff with that approach), or the washer is so soft
that it is mashed into the material being held.

Bob