Geometric Dimensioning and Tolerancing (GD&T) is a symbolic language for specifying part geometry. Used well, it tells the shop exactly what matters, more clearly than plus/minus tolerances.
Datums: your reference frame
Datums (A, B, C) are the surfaces or axes everything is measured from. Pick them as the functional locating features of the assembly.
Position over plus/minus
A position tolerance with datums controls where a hole sits relative to those datums—capturing true location better than separate X/Y callouts.
Common symbols
- Flatness / straightness: form of a single surface.
- Position: location of holes and features.
- Perpendicularity / parallelism: orientation.
- Profile: complex surface shape.
Why it helps
It separates critical control from cosmetic variation, so the shop inspects what counts and you pay only for that.
FAQ
Do I need GD&T on every part? No—use it where location and form truly matter.
Where to learn the calls? Our quality process explains how we apply it.
