Geometric tolerance

Geometric tolerance, defined through GD&T (geometric dimensioning and tolerancing), controls a feature's form (flatness, cylindricity), orientation (perpendicularity, angularity), location (position, concentricity) or runout, independently of its size dimension. It is specified with a feature control frame referencing a datum where applicable.

Why geometric tolerance often drives the process

Geometric tolerances often drive process and setup decisions more than dimensional tolerances do, since holding a position or perpendicularity requirement can require a specific datum-referenced setup that a plus/minus dimension alone would not.

Where it appears on the drawing

As a feature control frame: a boxed symbol, tolerance value and, where applicable, one or more datum references.

Common mistakes

Reading a geometric tolerance as if it were just a tighter dimensional tolerance; it controls a different aspect of the feature (form, orientation, location) and often forces a different, more specific measurement and setup strategy.

Is geometric tolerance the same as GD&T?

GD&T is the system and symbol set; geometric tolerance is what that system specifies, alongside dimensional tolerance for size.

Does a geometric tolerance need a datum?

Many do, such as position or perpendicularity; form tolerances like flatness typically don't reference a datum.

Why does a geometric tolerance affect setup?

Because meeting it, such as a position tolerance relative to a datum, can require holding the part in a specific orientation that a dimensional tolerance alone would not.