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GD&T Position

True Position

Position is one of the most useful and most complex of all the symbols in GD&T. The two methods of using Position discussed on this page will be RFS or Regardless of Feature Size and under a material condition (Maximum Material Condition or Least Material Condition). Position is always used with a feature of size.

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Datums in GD&T

A datum is theoretical exact plane, axis or point location that GD&T or dimensional tolerances are referenced to. You can think of them as an anchor for the entire part; where the other features are referenced from. A datum feature is usually an important functional feature that needs to be controlled during measurement as well.

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GD&T Symbols Profile of a surface

Profile of a Surface

Profile of a surface describes a 3-Dimensional tolerance zone around a surface, usually which is an advanced curve or shape...

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Maximum Material Condition (MMC)

Maximum Material Condition (MMC), is a feature of size symbol that describes the condition of a feature or part where the maximum amount of material (volume/size) exists within its dimensional tolerance.

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GD&T Form gdandtbasics.com

Flatness

GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing. The flatness tolerance references two parallel planes (parallel to the surface that it is called out on) that define a zone where the entire reference surface must lie.

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GD&T Symbol concentricity

Concentricity

Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis....

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GD&T perpendicularity symbol

Perpendicularity

Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line...

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RUNOUT circular GD&T symbol

Runout

Runout is how much one given reference feature or features vary with respect to another datum when the part is rotated 360° around the datum axis.

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Parallelism

Parallelism is a fairly common symbol that describes a parallel orientation of one referenced feature to a datum surface or line...

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Circularity

The circularity symbol is used to describe how close an object should be to a true circle...

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GD&T Symbol straightness

Straightness

The standard form of straightness is a 2-Dimensional tolerance that is used to ensure that a part is uniform across a surface or feature. Straightness can apply to either a flat feature such as the surface of a block, or it can apply to the surface of a cylinder along the axial direction. It is defined as the variance of the surface within a specified line on that surface.

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GD&T Symbol Runout

Total Runout

Total Runout is how much one entire feature or surface varies with respect to a datum when the part is rotated 360° around the datum axis...

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GDT Symbol cylindricity

Cylindricity

The Cylindricity symbol is used to describe how close an object conforms to a true cylinder...

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GD&T symbols feature control frame

Feature Control Frame

In GD&T, a feature control frame is required to describe the conditions and tolerances of a geometric control on a part's feature...

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GD&T Symbol symmetry

Symmetry

GD&T Symmetry is a 3-Dimensional tolerance that is used to ensure that two features on a part are uniform across a datum plane...

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GD&T Symbols Orientation angularity

Angularity

Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle...

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GD&T Symbol Least material Condition

Least Material Condition (LMC)

Least material condition is a feature of size symbol that describes a dimensional or size condition where the least amount of material (volume/size) exists within its dimensional tolerance...

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GD&T Symbol profile of a line

Profile of a Line

Profile of a line describes a tolerance zone around any line in any feature, usually of a curved shape...

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GD&T Symbol Regardless of Feature

Regardless of Feature Size

Regardless of feature size simply means that whatever GD&T callout you make, is controlled independently of the size dimension of the part. RFS is the default condition of all geometric tolerances by rule #2 of GD&T and requires no callout.

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