Printable reference · V0.6
GD&T Drawing Reference
A compact reference for common geometric-control families, datums and drawing-review logic.
GD&T Drawing Reference
Control families
| Family | Examples | Datum? |
|---|---|---|
| Form | Straightness, flatness, circularity, cylindricity | Normally no |
| Orientation | Parallelism, perpendicularity, angularity | Yes |
| Location | Position, concentric relationships where applicable | Usually |
| Profile | Profile of line / surface | Depends on intent |
| Runout | Circular runout, total runout | Yes |
Datum thinking
Primary datum
Usually the most functionally important stabilizing interface.
Secondary datum
Constrains the next degrees of freedom and reflects another functional contact/interface.
Tertiary datum
Completes the datum reference frame when required by function and inspection.
Drawing review prompts
- Are basic dimensions and geometric tolerances describing the same functional intent?
- Do datum features represent how the part is assembled, located or inspected?
- Are tight controls limited to characteristics that need them?
- Can the proposed tolerance actually be verified with the intended inspection method?
- Does the drawing specify the applicable drawing/GD&T standard and revision where your organization requires it?
DIVE-LD Engineering Learning · Educational reference only. Confirm project-specific requirements, governing standards and supplier capability before release.