Crosshead

Crosshead is a term with two primary meanings in English: a mechanical component in reciprocating engines and a typographic element used in publishing.

In mechanical engineering, particularly in steam locomotives and stationary steam engines, the crosshead is a sliding block that connects the piston rod to the connecting rod. The piston rod attaches to the crosshead, which then slides on guides mounted to the engine frame. The crosshead transmits the linear motion of the piston into the rotating motion of the crankshaft or driving wheel, while keeping the moving parts properly aligned. It is typically fitted with a bearing or slipper surface and requires careful lubrication and alignment to minimize wear and prevent binding under high loads.

In typography and publishing, crosshead refers to a short line of text used to mark a section boundary or to introduce the following content. It can function as a subheading or descriptor and is often set in a distinct type size or style from the body text. The exact form and placement of crossheads vary by era and publication, with some styles using them as decorative or organizational separators within a page. In modern practice, crossheads are less common than more explicit subheadings, but they appear in historical typography, journalism, and certain design approaches.

Etymology and usage notes: the term reflects the crosspiece nature of the part in machinery and the crosswise positioning of a heading element in layout. The two senses are distinct fields—engineering and publishing—sharing only the name.