Ratchets

A ratchet is a mechanical device that permits motion in one direction while resisting motion in the opposite direction. It typically consists of a toothed wheel called a ratchet wheel and a pawl or pawls that engage the teeth. When force is applied in the allowed direction, the pawl clicks over the teeth and the wheel advances. If a force attempts to move in the reverse direction, the pawl locks against the teeth, preventing back motion.

Common implementations include manual ratchets such as socket wrenches, where a handle provides repeated one-way turning, and ratchet straps, which use a ratcheting lever and a strap to tighten and secure loads. In rotating machinery, ratchets or one-way clutches are used in devices like bicycle hubs, winches, and indexers to permit rotation in one direction while blocking it in the other.

In addition to preventing reverse motion, ratchets can provide controlled, incremental movement in steps, as seen in some indexing mechanisms and antique clocks. The audible “click” often associated with ratchets results from the pawl snapping into place between teeth.

Key design considerations include the geometry of the teeth, the shape and range of the pawl, materials, and lubrication, all of which influence load capacity, efficiency, and wear. Maintenance focuses on keeping surfaces clean, free of debris, and ensuring pawls and springs function correctly; worn teeth or pawls can lead to slip or failure.

Historically, ratchet mechanisms have been used since early clockwork and machinery and have since become widespread in tools, securing devices, and various mechanical systems.