## What is a feature control frame?

A key component of geometric dimensioning and tolerancing (commonly referred to as GD&T). On engineering blueprints, the feature control frame consists of a symbol to identify the type of tolerance, the amount of tolerance and reference datums if applicable.

## How to read a feature control frame

A feature control frame is read from left to right. It reads “Type of control” of “Tolerance” to Datum. It should be noted that if a diameter symbol is present before “Tolerance” then it indicates the shape of the tolerance zone is cylindrical.

## Examples

True position of 0.2 to datums A and B

Perpendicularity of 0.001 to datum A

Cylindricity of 0.001

Circular runout of 0.010 to datum A

## Composite feature control frame

A composite feature control frame controls both a pattern on a part and the location of individual items in the pattern.

The upper section of a composite feature control frame specifies the tolerance for the pattern to the overall part.

The lower section specifies the tolerance for individual features to the pattern. In the example of a bolt hole circle, the upper section controls the tolerance for the location of the bolt hole circle on the part. The lower section would control how closely the individual holes must follow the pattern.

## Feature control frame symbols

For more information see our GD&T Symbols Quick Reference

## Basic dimensions

Basic dimensions are identified by a rectangular frame around the dimension.

They are dimensions that are theoretically exact. They do not have a tolerance themselves (general blueprint tolerances do not apply).

Instead they are controlled by another characteristic. This is often seen with positional tolerances such as the true position of a hole. The hole location will be specified as basic dimensions.

A true position tolerance will then be assigned to the hole which will control how far off the nominal location the hole can be.

## Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

## GD&T Symbols Quick Reference

A cheat sheet type reference for the most common GD&T symbols.

See also our GD&T Font – GD&T Keyboard Shortcuts List

 Symbol Name Description Straightness Straightness is how close to a straight line a feature is. Flatness Flatness is how flat a feature is. All points on the feature must lie within two parallel planes that are spaced the tolerance width apart. Circularity Often called roundness. Circularity refers to how close to a perfect circle a single location is. Circularity is at one location. This can be thought of as a single circle on a cylinder. Usually circularity would be checked at multiple locations along the cylinder. This cylinder can be the inside of a hole, the outside of a shaft or various other features. Cylindricity Cylindricity is the same as circularity (often called roundness) with the exception that the requirement applies across the whole surface instead of at a single location. Cylindricity works to control taper whereas circularity does not. Parallelism Parallelism refers to how close to 180 degrees two surfaces are. Perpendicularity Perpendicularity is how close to 90 degrees two features are. This can be any combination of planes or axes. Angularity Angularity is the same as perpendicularity with the exception that the two features are not at 90 degrees to one another but instead at a different specified angle. Concentricity Concentricity is how close the axes of two features run together. True Position True position is a theoretically exact location of a feature. Symmetry Symmetry is the same as concentricity but is applied to features that aren’t round. This means that the axes or centers of two features must run together. Profile of a Line Profile of a line controls the shape of a cross section of a feature. It can control size, form and location. Profile of a Surface Profile of a surface is similar to the profile of a line tolerance but it controls the entire surface instead of a single cross section. Circular Runout Circular runout controls the runout in a single location of a circular feature such as a cylinder. Total Runout Total runout controls the runout of an entire surface of a circular feature instead of at a single location. When compared to circular runout, total runout would check the entire cylinder.

## Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Get the Best GD&T Training Available

## Related Articles

For more information see these related articles:

Facebook Twitter Youtube

A cheat sheet type reference for the most common GD&T symbols.

See also our GD&T Font – GD&T Keyboard Shortcuts List

 Symbol Name Description Straightness Straightness is how close to a straight line a feature is. Flatness Flatness is how flat a feature is. All points on the feature must lie within two parallel planes that are spaced the tolerance width apart. Circularity Often called roundness. Circularity refers to how close to a perfect circle a single location is. Circularity is at one location. This can be thought of as a single circle on a cylinder. Usually circularity would be checked at multiple locations along the cylinder. This cylinder can be the inside of a hole, the outside of a shaft or various other features. Cylindricity Cylindricity is the same as circularity (often called roundness) with the exception that the requirement applies across the whole surface instead of at a single location. Cylindricity works to control taper whereas circularity does not. Parallelism Parallelism refers to how close to 180 degrees two surfaces are. Perpendicularity Perpendicularity is how close to 90 degrees two features are. This can be any combination of planes or axes. Angularity Angularity is the same as perpendicularity with the exception that the two features are not at 90 degrees to one another but instead at a different specified angle. Concentricity Concentricity is how close the axes of two features run together. True Position True position is a theoretically exact location of a feature. Symmetry Symmetry is the same as concentricity but is applied to features that aren’t round. This means that the axes or centers of two features must run together. Profile of a Line Profile of a line controls the shape of a cross section of a feature. It can control size, form and location. Profile of a Surface Profile of a surface is similar to the profile of a line tolerance but it controls the entire surface instead of a single cross section. Circular Runout Circular runout controls the runout in a single location of a circular feature such as a cylinder. Total Runout Total runout controls the runout of an entire surface of a circular feature instead of at a single location. When compared to circular runout, total runout would check the entire cylinder.

## Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!