Articles related to GD&T symbol rules and walk-through examples of GD&T Symbols and their uses
In this question line video, Brandon reviews the differences between the GD&T callouts for circularity, circular runout, and total runout. To examine the differences in these concepts it is helpful to first review the Geometric...
Does Runout or Size Control the Circularity/Form Error in GD&T? (Answer: It Depends) In this article video, we aim to answer how Runout is used to control the form/shape/circularity/cylindricity on a cylinder. It also...
Check out this question brought up about Flatness in our GD&T Fundamentals Course. We get a lot of questions about when flatness can be applied and how datums can be used with this. There are...
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.
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.
The circularity symbol is used to describe how close an object should be to a true circle...
Parallelism is a fairly common symbol that describes a parallel orientation of one referenced feature to a datum surface or line...
The Cylindricity symbol is used to describe how close an object conforms to a true cylinder...
Profile of a surface describes a 3-Dimensional tolerance zone around a surface, usually which is an advanced curve or shape...
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.
Concentricity, is a tolerance that controls the central derived median points of the referenced feature, to a datum axis. Concentricity is a very complex feature because it relies on measurements from derived median points as opposed to a surface or feature’s axis.
Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line...
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...
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.
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...
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.
In GD&T, a feature control frame is required to describe the conditions and tolerances of a geometric control on a part's feature...
Profile of a line describes a tolerance zone around any line in any feature, usually of a curved shape...
Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle...
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.
