One method of rust removal that I believe has not yet been mentioned is
to remove rust by electrolysis.  Google "rust removal by electrolysis"
and you'll get a ton of links.  An example would be:
http://antique-engines.com/electrol.asp

This site deals with larger objects than itty-bitty screws, but you'll
get the idea.  The author makes a point that using stainless steel for
one of the electrodes, which is common practice, is hazardous as toxic
chromium salts are leached into the electrolyte making it illegal to
discard down the drain in addition to exposing yourself directly to the
hazard.  There are much safer easy-to-obtain electrodes, iron re-bar
being the example given.  I suggest that for smaller objects where
speed is not an issue it would be wise to use much less current than
is recommended in the above link.

If you have a tank large enough, this method also works for steel
musical box discs.  The results are spectacular but the printing is
removed.   :( 

By the way, the cleaned object is left so clean that it will rust again
almost instantly if it is not given a light protective coat to keep the
air away.

Regarding large items, the site above gives some nice photos of the
restoration of an antique "mud pump."

Jim Heyworth,
Sechelt, British Columbia, Canada