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ruling pen[′rül·iŋ ‚pen]
a drafting instrument for drawing lines 0.08 to 1.6 mm thick, as with India ink. A road pen makes it possible to draw simultaneously two parallel lines, of the same or different thickness, along a ruler or a French curve; the two lines are 0.5 to 8 mm apart. A single or double curve-point pen is used for drawing single or double (0.5–5 mm apart) curved lines freehand (without a French curve). Ruling pen holders are made of plastic or sometimes steel; the pen points are made of steel or high-impact plastic reinforced with steel blades. The thickness of the lines is regulated.