A11 · Reference edition 2026.11
The 3-2-1 layout concept — Definition and boundaries
Three, two and one contact groups describe a conceptual constraint arrangement for a suitable rigid part. Contact geometry still needs review.
Scope and purpose
Start by separating the named concept from adjacent concepts. Use the observation below to identify the question the record is intended to answer. Read the caution before applying the example. A definition is useful only when another reader can tell what falls outside it.
Working notes
This reference collection concerns light, offline dimensional-inspection layouts. It brings locating concepts, component descriptions and revision records together without substituting for an engineered fixture design. The drawings are original explanatory diagrams. Reference IDs identify documents, not commercially tested products. Read the scope and limitations alongside each example, and keep the actual part drawing and inspection requirements available when reviewing a proposed layout.
Practical example
Sketch three primary supports before adding secondary and tertiary locators.
| Reference record | Interpretation |
|---|---|
| A11 | The 3-2-1 layout concept |
| Scope and purpose | Three, two and one contact groups describe a conceptual constraint arrangement for a suitable rigid part. Contact geometry still needs review. |
| Limits and interpretation | Thin walls and flexible parts need analysis beyond the rigid-body sketch. |
Review checklist
Write a one-sentence scope statement; identify a neighbouring concept; record what the example does not establish.