Angularity controls how far a surface or an axis may deviate from a stated angle to a datum. It sits alongside perpendicularity and parallelism as the third orientation control, and it differs from a plus minus angular dimension in a way that matters: the tolerance zone is a distance, not an angle, so it does not grow as the feature gets longer.
The basic angle and the zone
The angle itself is stated as a basic dimension, boxed and untoleranced, because the geometric callout carries the tolerance. The zone is two parallel planes separated by the tolerance value and oriented at that basic angle to the datum, and the whole surface must lie between them. For an axis the zone is usually a cylinder at the basic angle.
Why it beats a toleranced angle
A plus minus angular tolerance defines a wedge shaped zone that gets wider the further you go from the vertex, so the permitted deviation at the far end of a long face is much larger than at the near end. A geometric angularity zone is a constant width whatever the length, which is nearly always what the function actually requires.
How it is inspected
The part is located on its datums, and the controlled surface is measured across its extent, either on a coordinate measuring machine or with a sine plate and an indicator on a surface plate. As with every orientation control, the result depends on the datum being set up as the drawing specifies, and a datum scheme that does not match the fixture produces a meaningless number.
Related controls
Perpendicularity is angularity at ninety degrees and has its own symbol. Parallelism is angularity at zero degrees and likewise. Where the surface's own form also has to be controlled more tightly than the orientation, profile of a surface does both at once. Most drawings need only perpendicularity and parallelism, with angularity for the genuinely angled faces.
Questions people ask about angularity gd&t
What does angularity control?
How far a surface or axis may deviate from a stated basic angle to a datum, within a tolerance zone of constant width.
Why is the angle basic?
Because the geometric callout supplies the tolerance. A boxed basic dimension carries no tolerance of its own and defines the theoretical orientation.
Angularity or a plus minus angle?
Angularity, in most cases, because its zone is a constant width rather than a wedge that widens along the face, which is what function usually needs.
Does angularity need a datum?
Always. It is an orientation control and has no meaning without something to be at an angle to.