crosshead

right|thumbnail|A crosshead as part of a reciprocating piston and slider-crank linkage mechanism. thumb|Cylindrical trunk guide thumb|Hudswell Clarke Nunlow; crosshead and two slide bars

In mechanical engineering, a crosshead is a mechanical joint used as part of the slider-crank linkages of long stroke reciprocating engines (either internal combustion or steam) and reciprocating compressors to eliminate sideways force on the piston. The crosshead also allows the connecting rod to move freely outside the cylinder. Because of the very small bore-to-stroke ratio on such engines, the connecting rod would hit the cylinder walls and block the engine from rotating if the piston were attached directly to the connecting rod as in a trunk engine. Therefore, the longitudinal dimension of the crosshead must be matched to the stroke of the engine.