Most times parallels are used with a vise on a milling machine, to stand a small part above the top of the jaws. Used in pairs, mostly. The two long edges are "Parallel". But they may not be flat, so can only be used in that orientation.
was strolling around a new Harbor Freight store the other day and I came
<BR>across a small box containing twenty little metal plates. The box was
marked <BR>Parallels.<BR><BR>I asked the folks working there what they were,
but all I got was shoulder <BR>shrugs and "I dunno's".<BR><BR>When I returned
home, I looked up these Parallels on Harbor Freight's web <BR>site (item
number: 789-5VGA), however their description was obviously meant <BR>for some
one who already knew what the little things were used