The following a common reasons one should apply GD&T principles:
1. Part features are critical to function or interchangeability.
2. When functional gauging techniques are desired.
3. When a common reference (origin) or datum is required to ensure communication is consistent between design, manufacturing and inspection.
4. When a standard interpretation or tolerance is not already implied.
5. Simplify tolerance analysis.
6. Replace complex or long geometry requirement description notes with a single geometric symbol.
Engineer Edge offers practical industry sensitive geometric dimensioning and tolerancing (DG&T) training on site and public seminars.