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GD&T Geometric Dimensioning symbols

GD&T symbols are used to define the relationships between a part features and measurement references.

GD&T symbols


Straistraighness symbolghtness

Straightness control of a feature in GD&T can be surface Straightness or an axis Straightness of a cylinder. This is usually called out with an maximum material condition.
Flatness
flatness symbolGD&T Flatness is a common symbol that references how flat a surface is regardless of any other datums or features.
Circularity
circularityThe circularity also called roundness. This symbol is used to describe the required roundness of an object.
Cylindricity
cylindricityThe Cylindricity symbol is used to describe an object conforms to a cylinder axis. a cylindrical feature to ensure that it is round enough and straight enough along its axis.

Profile of a Line

profile of a lineProfile of a line describes a tolerance zone around any curved profile or shape. It is usually called out on a profile surface, like a radius on a part, it specify how much that cross-section could vary from a true curved radius.

Profile of a Surface

profile of surfaceProfile of a surface is similar to the Profile of line, but it controls the entire 3-Dimensional tolerance zone around a surface, the entire surface has to fall within the tolerance zone.
Angularity
angularity symbolAngularity is the symbol that control orientation of one feature to another at a referenced angle.
Perpendicularly
perpendicularityPerpendicularly is a tolerance that controls Perpendicularly between two 90° surfaces, or between a surface and hole axis.

Parallelism

parallelisum Parallelism is a tolerance that controls parallelism between two surfaces or features.

 

Position
true positionPosition is the most commonly used symbol in GD&T, The True Position is the exact coordinate, or location allowable in the defined dimensions.
Concentricity
concentricityConcentricity is a tolerance that controls the central axis of the referenced feature, to a datum axis.
Symmetry
symmetric Symmetry is the tolerance that is used to ensure two features on a part are uniform across a datum plane.

Circular runout

runoutRunout is the total variation that the reference surface can have when the part is rotated around the datum axis.

Total runout

Total Runout controls the value of a feature when the feature is rotated around the datum axis and along the axis. Both radial variation and axial variation are measured within the tolerance.

 

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