ruby

In metal type, ruby was a fixed body size of 5½ points, sitting between pearl (5 point) and nonpareil (6 point) in the traditional typographic scale. Like all sizes in the old points system, ruby was a physical dimension: a piece of type metal cast to that height, measured from baseline to top of the tallest sorts. Printers would order ruby sorts, lowercase letters, figures, punctuation, to compose text at that size, and these pieces would interlock with sorts of other sizes in the same job only by careful line-spacing or by casting them on different body sizes.

Ruby saw use in newspapers, reference books, and dense body text where a size smaller than nonpareil but larger than pearl was wanted. Because 5½ points falls awkwardly between two round units, ruby was never as common as nonpareil or brevier (8 point), and regional usage varied. British foundries were more consistent in offering it than American ones.

Why the name disappeared

The point names, ruby, pearl, nonpareil, minion, bourgeois, and the rest, were mnemonics from an era before standardized measurement. They derived from specific typefaces or foundry practices, not from logical units. Once phototypesetting arrived in the mid-20th century, type could be set at any size to the fraction of a point, making fixed sizes redundant. The old names, tied to physical metal, became museum vocabulary.

Today ruby is encountered only in historical texts, specimen books, and in the typographic memory of letterpress practitioners. Anyone setting text in digital systems will never encounter the ruby size by name, though 5.5 points remains a selectable size in software. The term survives as a footnote to a technology that assumed type came in discrete, permanent increments.