ratsche

Ratsche, in German commonly translated as ratchet, refers to a class of mechanical devices that allows motion in one direction while resisting motion in the opposite direction. The basic form consists of a ratchet wheel with asymmetrical teeth and a pawl that engages the teeth. When torque is applied in the drive direction, the pawl catches the teeth and the mechanism advances; reverse motion is prevented or limited by the pawl wedging against the teeth, producing locking or controlled stepping.

There are several variations. A simple ratchet uses a fixed pawl and a ratchet wheel, often with a spring that returns the pawl to engagement after a step. More complex designs include bi-directional ratchets that can switch the engaging side or use a different mechanism, such as a sprag clutch, to allow motion in one direction while blocking the other. Some systems employ a freewheel behavior, where only forward movement is transmitted, while rearward movement is free or minimally resisted.

Common forms and applications include ratchet wrenches and other hand tools, which convert rotating handle force into incremental socket or bolt movement while preventing backward rotation. Ratchet mechanisms also appear in cargo securing systems like ratchet straps, winches and hoists, clocks and timing devices, and various indexing or positioning mechanisms in machinery. In engineering design, ratchets enable controlled, stepwise advancement, maintenance of position under load, and the conversion of continuous rotation into discrete movement.

Etymology-wise, the term originates from the German word ratsche, related to the concept of a gear tooth and a locking element. The concept has been adopted broadly in mechanical engineering and applied in many industries.