# Principal direction

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> Source: https://en.wikipedia.org/wiki/Principal_direction
> Source revision: 1051501910
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A **principal direction** can refer to one of the following:

- [Principal directions (geometry)](/source/Principal_directions_(geometry)) - In differential geometry, one of the directions of principal curvature.
- [Principal directions](/source/List_of_gear_nomenclature#Principal_directions) - a term used in gear nomenclature.
- In stress analysis, a set of axes where the normal stress vector is maximized. See [Stress (mechanics)](/source/Stress_(mechanics)#Principal_stresses_and_stress_invariants)

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Adapted from the Wikipedia article [Principal direction](https://en.wikipedia.org/wiki/Principal_direction) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Principal_direction?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.