Polygon profile

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Bottom bracket with square shaft for mounting the pedal crank on the bike

The polygonal profile is a shaft or hub that corresponds in cross-section to a polygon , but whose corners are rounded. Such profiles are particularly popular in mechanical engineering as a form-fitting shaft-hub connection for maximum torques.


The shaft is flattened on several sides, which changes its cross-section from round to polygonal. A hub with a suitably designed inner cross-section can now be pushed onto the shaft. In addition, the polygon profile of the shaft can be made conical. This results in a backlash-free seat with additional frictional connection when a corresponding hub is pressed on .

Special features

It has great centering accuracy because it is self-centering. The power transmission practically free of notch effects enables the transmission of significantly higher torques compared to the parallel key connection with the same size . The polygon shape is almost exclusively ground on a round shaft. This is an extremely expensive process and is often the reason why a cheaper solution is chosen. Furthermore, there are limits to miniaturization due to this manufacturing process. An exception to this is the drawing of miniature polygon waves. Thanks to this drawing process, even the smallest polygon waves can be produced efficiently.


See shaft-hub connection