double letter

In letterpress printing, a double letter is a single piece of metal type that carries two characters on its shank instead of one. The two letters are cast together as a unified block, sharing the same height of type (typically 0.918 inches for standard body size) and occupying less horizontal space than if the two letters were set separately. Common double letters include ff, fi, and fl, though others like ffi and ffl also exist as triple characters on one body.

The primary purpose of a double letter is to solve a spacing and alignment problem that occurs with certain letter combinations. When an f sits next to an i, l, or another f in many typefaces, the combinations look awkward or create kerning issues because the crossbar or dot of the following letter intrudes into the space above the descending stroke. By casting them on a single shank, the type founder controls the exact spacing and prevents these collisions. The result is a smoother, more professional appearance on the printed page.

Double letters are not universal to all typefaces. Their necessity depends on the specific design of the individual letters and the amount of overhang in the typeface design. A condensed font with minimal overhang may need fewer doubles; a flourished or script font may require many more. Foundries typically supply double letters as part of a complete font, though custom doubles can be cast for special purposes. In practice, a compositor selects the appropriate double letter from the type case when setting text, treating it exactly as they would a single character.

Distinctions and related terms

Double letters should not be confused with ligatures in the modern typographic sense. While both involve multiple characters on one body, a true ligature is a fusion of letterforms into a single visual unit, whereas a double letter is simply two standard characters positioned next to each other on one shank. Additionally, some foundries distinguished between doubles (two separate characters on one body) and ligatures (two characters merged into a connected form). The terminology varied by foundry and region.

The need for double letters diminished with the rise of photo-offset printing and digital type, where kerning pairs and automatic spacing became standard features built into the software or film. In contemporary letterpress revival and fine printing, however, double letters remain essential tools for anyone setting metal type by hand, offering the only reliable way to achieve proper spacing in these historically problematic combinations.