Hello Joel, and MMD.  Yes, you can use those machines to clean screws,
as they are used, and indeed built specifically, for cleaning brass
shell casings prior to reloading.  The really nice ones use a vibrating
action rather than a rotating drum, and do not harm the metal when used
with the proper medium.

The medium used to polish brass is (if memory serves) ground corn cobs,
_not_ sand or other hard minerals like corundum.  Those things are used
to cut rock, and could damage the screws.

Take a look at a copy of American Rifleman, or a similar shooting
magazine.  The ads for these neat machines appear often.

Regards,
Bob Loesch
Northern California
http://home.jps.net/~rrloesch/index.htm