GD&T Symbols Quick Reference

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 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 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 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.