# Concentricity Tolerance : GD&T Basics

Concentricity tolerance controls the central axis of a cylinder or sphere with respect to datum plane/axis. It also controls the median points of a cylindrical parts. For example transmission gears. Refer this article to understand the basics of geometric tolerance.

##### Representation

Datum plane, surface or axis  is required to define concentricity tolerance. LMC and MMC modifiers are not applicable with concentric tolerance.

##### Tolerance Zone

Concentricity tolerance creates a 3-dimensional cylindrical tolerance zone around datum axis. All central points of the circular feature must lie in this tolerance zone.

##### How To Measure ?
Concentricity tolerance is very difficult to measure. Therefore runout and position tolerance are used as alternative.  Concentricity of a cylindrical part is measured in following steps.

Step-1 : Identify and fix the part on datum.

Step-2 : Plot controlled surface outer profile. CMM can be used to create the profile.

Step-4: Determine the central points of plotted profile at various cross sections.

Step-5: Verify position of central points. All points shall lie within given cylindrical tolerance zone.

#### Conclusion

To sum up, Concentricity tolerance controls the central axis of a cylinder or sphere with respect to datum plane/axis. It is very difficult to measure. Therefore runout and position tolerance are used as alternative

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