ClipArt ETC
"A draftsman's instrument for ruling parallel lines. It consists of a triangle so attached to a straight-edge that it can be moved back and forth on it a distance predetermined by the adjustment of a set-screw. a, a straight-edge; b, triangle moving on <i>a</i> for a distance determined by the set of the micrometer scale <i>c</i>; d, spring for releasing triangle and keeping it in the end of its slot." -Whitney, 1889

Section Liner, A Draftsman's Tool

"A draftsman's instrument for ruling parallel lines. It consists of a triangle so attached to a straight-edge…