pinions

Pinion (plural pinions) is a term used in mechanical engineering to denote a small gear that meshes with a larger gear or with a rack. In a gear train, the pinion is usually the driving gear, and the gear ratio is determined by the numbers of teeth on the pinion and the mating gear. Pinions are designed with standardized pitches and modules, and the teeth must be compatible to ensure smooth meshing. In clocks, automotive transmissions, and other machinery, the pinion transmits torque from its shaft to a wheel or rack. A pinion may itself be mounted on a shaft and carry the eventual driven gear as part of a compound gear train.

Pinion can also refer to the wing of a bird or to a group of primary flight feathers in some contexts; in ornithology the term has been used to describe the outer portion of the wing or the primary feathers, though usage varies by region and author.

Pinioning is the practice of clipping or removing part of a bird’s wing feathers to prevent flight; while historically common for domesticated birds and show birds, it is controversial due to welfare concerns and is restricted by law in many places. Alternatives include secure enclosures, enrichment, and trained handling.

Examples of gear use include a pinion with a known tooth count engaging a larger gear to produce a desired reduction or increase in speed. In practice, the accurate matching of tooth size, pressure angle, and material is essential for reliable operation of a pinion-based drive system.