Parallels are used to support a workpiece
when clamping it in a milling vise. They are pairs of steel rectangles that
are accurately matched in height. In use, the parallels are placed adjacent
to each jaw of the milling vise and the workpiece is supported by the
parallels such that the workpiece is exactly parallel with the base of the
milling vise, and thus with the milling table. Parallels come in sets in
which the length and thickness are common to all, with pairs varying
incrementally in height.
