vicesimo-quarto

Vicesimo-quarto, abbreviated 24mo, is a book size produced by folding a sheet of printing paper into twenty-four leaves, or forty-eight pages. The term comes from the Latin for "twenty-fourth": one sheet folded and cut yields twenty-four separate leaves. This produces a small, portable format roughly 2.5 inches by 5 inches, though exact dimensions depend on the parent sheet size and how the signatures are trimmed after folding.

The format sits at the extreme end of practical bookbinding. Most trade printing works in octavo (8vo), sixteenmo (16mo), or thirty-twomo (32mo); vicesimo-quarto is rarely specified today except for novelty editions, miniature reference books, or heritage reprints. Each leaf is extremely thin once the nested folds are separated and cut, making the paper selection critical. The binder must use stock of at least 80 gsm to avoid excessive show-through and handling damage.

Creating a 24mo book requires careful signature planning. The printer must impose twenty-four pages on a single side of the parent sheet before folding. A single misregistration compounds across all twenty-four leaves. The collating sequence becomes complex: after the first fold, the sheet contains two sets of twelve nested leaves; subsequent folds halve the leaf count again until the final cut separates them. Any error in fold sequence or trimming ruins the entire sheet.

The format's historical role was practical: before paperbacks, publishers used small formats for pocket editions and travel books. Today, vicesimo-quarto appears mainly in limited editions, miniature libraries, and specialized reference sets where the small size is a feature rather than an economy. The format demands skilled labor and careful material selection, making it too expensive for mass market use despite its compact appeal.