cranks

Cranks are components in mechanical systems consisting of a rigid arm attached to a rotating shaft at an angle to convert between rotary and linear motion. The term covers a range of devices, from small handles on a door to large shafts in motor engines.

In engines and machinery, a crankshaft carries one or more crankpins offset from the axis. As the shaft rotates, the crankpins move the connecting rods and pistons, generating reciprocating motion and, ultimately, rotary output. The distance of the offset (the crank throw) defines the stroke of the piston, while the geometry of the crank and connecting rod influences balance and torque transmission.

In bicycles and similar transmission systems, the crank refers to the crank arms that connect pedals to the bottom bracket, typically forming part of the crankset along with the chainrings. The length of the crank arms, the number of chainrings, and the bottom-bracket geometry affect pedaling efficiency and leg position.

Other uses include the manual-crank handle used to operate mechanisms such as winches, faucets, or valves. In engineering terms, an eccentric is a related concept where the axis of rotation is offset to produce oscillating or sliding motion rather than full rotary movement.

In colloquial use, cranks are people characterized as eccentric or irrational, often associated with holding controversial or pseudoscientific beliefs. The label is pejorative and its application varies by context.