Connecting rod
（重定向自Main rod）
![piston (top) and connecting rod from typical automotive engine (scale is in centimetres)](/Images/godic/202501/25/Piston_and_connecting_rod5702.jpg")
![Scheme of the Roman Hierapolis sawmill, the earliest known machine to combine a connecting rod with a crank.[3]](/Images/godic/202501/25/Römische_Sägemühle.svg5702.png")
![Beam engine, with twin connecting rods (almost vertical) between the horizontal beam and the flywheel cranks](/Images/godic/202501/25/Twin_Beam_Engine5702.jpg")
![Crosshead of a stationary steam engine: piston rod to the left, connecting rod to the right](/Images/godic/202501/25/Radevormwald_Dahlerau_-_Wülfingmuseum_-_Dampfmaschine_05_ies5702.jpg")
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts reciprocating motion into rotating motion.
Connecting rods may also convert rotating motion into reciprocating motion. Historically, before the development of engines, they were first used in this way.