# What’s The Difference Between Runout And Concentricity?

Concentricity limits how asymmetric the shaft will be in relation the datum axis. If the shaft is oval without being a perfect circle, it can still considered concentric. By imposing diametrical symmetry, it regulates mass balance about the datum axis. It does not influence the size or taper of the shaft. At the same axial location along the datum axis, it compares the radius on one side of the shaft to the radius on the other side of it.

Runout limits how the unbalanced circular or spherical shaft relates to each datum point located along the shaft. In the scenario where the shaft may be perfectly circular or round, if its axis deviates from the datum point, it will be considered a runout. However, the shaft size is not caused by the runout and runout has no control over the other forms, but only affects the variance of the radius-to-datum in each location.

## How Similar Are the Results?

Position specifies the volume in which the shaft’s surface must remain. The shaft surface’s volume must remain in is determined by the shaft’s maximum permissible diameter alongside the tolerance of the position. The volume the axis must retain the tolerance of position and the maximum material tolerance allowed. The surface approach is the one to use. Any approach should produce relatively comparable results for an actual component, and they are also mathematically equivalent.

## What Is the Difference between Runout and Concentricity?

Concentricity is the circular form of geometric dimensions and tolerance symmetry, while the runout combines both circularity and concentricity. The runout will equate to concentricity if the component is perfectly spherical and round. However, what is circularity in this text? Circularity would determine the form, orientation, and location and usually cannot be referenced to the datum axis. However, the only exception would be when the size tolerance is tighter than the runout tolerance.

Concentricity considers how a cylindrical shape is positioned on a theoretical axis. In contrast, the runout considers how the target deviates from the dimensions of a circle when it is perfectly positioned on the rotation axis. However, when the part is measured using a similar cross-sectional plane, this is considered a case of coaxiality, as the internal diameter and outer diameters of the shaft or tube are compared.

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