The rule about hairline rules (QuarkXPress 5/6/7)

While hairline rules may look great onscreen and okay printed on a desktop printer, they probably won’t look so good when printed on an output device that prints over 300 dpi. For this reason, it’s best to avoid using the Hairline option (defined as a zero width line) when drawing rules or frames in QuarkXPress. To access the Hairline option, open the Modify dialog box (Item > Modify), click on the Line tab if you have a line selected, or the Frame tab if you have a frame selected. Then, click on the Line Width pop-up menu. To ensure your rules print on any device, always define their Line Width as no less than 0.25 points.