type-high
Of the standard height of a line of type.
type-high: the universal baseline height for printing
Type-high is the fixed vertical dimension from the bottom of a piece of metal type to the top of its printing surface. In the Anglo-American printing system, this height is precisely 0.918 inches (23.3 mm). Any type, plate, block, or cut that prints must stand at exactly this height when locked into a printing press, or the impression will be uneven and unusable.
The standard emerged because hand-set metal type had to stack consistently in a compositor's galley and lock rigidly in the printing chase. If one piece stood even 0.05 inches taller or shorter, it would either tower above the printing surface and suffer immediate damage, or sit below and print invisible. Type founders cast their bodies to this single dimension so that a page of type from different foundries would print as one. The metric system uses a different standard, 23.4 mm, creating a persistent incompatibility between Anglo-American and continental European equipment.
Beyond metal type
The concept expanded beyond cast type to any printing surface. Photographic plates, wood or steel engravings, stereotype plates, and electrotype duplicates all had to reach type-high to work in a standard flatbed press. Linotype and Monotype machines cast slugs to type-high automatically. Printers kept brass furniture and wooden spacing material in graduated thicknesses to build up underlays that would bring short elements to the correct height.
Letterpress operators verified type-high using a metal gauge or by running a finger across the locked form to feel whether any piece proud or shy. A gauge that was consistently off by even a few thousandths would ruin entire print runs through uneven pressure. Some foundries warranted their type to hold within 0.002 inches of type-high.
Modern offset and digital printing eliminated the mechanical need for type-high, but the term persists in digital typography as a reference dimension for line spacing and grid systems. For anyone setting metal type today, understanding type-high remains non-negotiable: it is the single constraint that makes letterpress possible.