Spindle

Spindle is a term used in biology, textiles, and mechanical engineering to denote a slender, rod-like element involved in function, formation, or rotation.

In cell biology, the mitotic spindle is a microtubule-based structure that organizes and separates chromosomes during cell division. It forms in prophase from spindle poles and microtubules. Kinetochore microtubules attach to kinetochores on chromosomes, while interpolar and astral microtubules help align and separate chromatids. In animals, spindle poles typically derive from centrosomes containing centrioles; many plants and fungi assemble spindles without centrioles. The spindle disassembles after telophase.

In textiles, a spindle is a rod or pin on which fibers are wound and twisted to form yarn. A simple drop spindle is portable, and spindles are also components of spinning wheels, where the wheel’s rotation twists fibers and winds the yarn.

In machinery, a spindle is the rotating axis that carries a tool or a workpiece in machine tools such as lathes and milling machines. Spindles must provide precise rotation, concentricity, and rigidity, and may be belt-driven, gear-driven, or direct-drive, with various bearings and cooling systems.

The term also appears in pathology to describe spindle-shaped cells or fibers, and in general usage to denote elongated, spindle-like objects.