CRANK, literally a bend or turn, is used in mechanics particularly to denote a contrivance for converting a rotatory into a reciprocating motion, and vice versa, either by means of a simple rectangular bend at the extremity of an axis, or by a double bend in any other part of its rectilinear length, thus A diagram of a crank mechanism showing a horizontal axis with a rectangular bend at one end and a vertical rod attached to the center of the bend.. As the axis revolves, the crank describes the circumference of a circle, and gives the rod attached to it a reciprocating motion. There are various modifications of this useful contrivance. See MECHANICS, and STEAM-ENGINE.