space rule
A fine, thin, short metal rule of the same height as the type, used in printing short lines in tabular matter.
space rule: thin metal strip for printing short lines in tables
A space rule is a strip of metal type-high material, typically made from brass or steel, that prints a thin line when locked into a forme with letterpress type. Unlike a full-length rule that spans an entire page width, a space rule is cut short, often between 1 and 4 inches long, and serves to separate rows or columns in tabular composition. It is set flush with the surrounding type at exactly type height (0.918 inches in points) so the printing surface registers level on the platen.
Space rules come in various point widths, commonly 1, 2, 4, 6, 8, and 12 points, and may be supplied with feet cast underneath for additional support within a chase. They are handled as loose metal furniture rather than as part of a composed metal line, which makes them faster to insert and remove than casting rules into stereotype plates. The term "space" derives from their function as logical separators between data fields or records, not from their physical length.
Letterpress compositors relied on space rules to build tables, invoice forms, and columnar reports with horizontal dividers. A table might use multiple space rules stacked vertically to create a grid, with leads (strips of 2 to 6 points thick) providing the vertical spacing between lines of type. The rules printed as solid lines because they carried ink on their upper surface, while leads remained silent.
Damage or wear to a space rule results in broken or faint lines in print. A dented or burred rule will cause uneven pressure and patchy inking. Rules that are even slightly out of type height (proud or sunken) will print inconsistently or not at all, requiring the compositor to replace them or build compensating backing materials underneath.
Space rules became obsolete as offset lithography displaced letterpress in commercial printing from the 1950s onward. In that process, rules are drawn or photographed into artwork rather than set as physical objects. Today they persist only in small-format hand-printing shops and among hobbyists who maintain letterpress equipment.