shaft

A shaft is a term used in several technical and everyday contexts to denote a long, slender, central, or supporting element. In engineering, architecture, mining, and biology, the word describes a piece that transmits motion, bears load, provides access, or forms the core of a structure.

In mechanical engineering, a shaft is a rotating cylindrical component that transmits torque and rotation between machine parts, such as gears, pulleys, or rotors. Typical shafts are made of metal and may be solid or hollow. They may be machined, splined, or keyed to accept components and to resist bending and torsion.

In architecture and classical design, the shaft refers to the vertical, cylindrical part of a column between its base and capital. The term is also used loosely to describe vertical channels in other structures, often treated as a structural or decorative element rather than a load-bearing member.

In mining, construction, and civil engineering, a shaft is a vertical or near-vertical passage that connects the surface with subsurface levels. Shafts provide access for workers and equipment, serve ventilation and drainage, and house lifting systems. They are typically sunk or bored and may be lined with concrete or steel.

In anatomy, the shaft of a long bone, called the diaphysis, is the central cylindrical region between the ends where the bone is thickest and lightest. It contains a marrow cavity and is mainly composed of compact bone, designed to withstand bending and torsion.

Other uses include the hair shaft, the visible part of a hair extending from the skin, and the shaft of a tool or instrument, which denotes its central axis.