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Free tool
GD&T Feature Control Frame Checker
Build a feature control frame and see right away whether it is legal under ASME Y14.5-2018 (or 2009), and why. No signup. It checks the frame's grammar: symbol, tolerance, modifiers and datums. It does not judge whether the value suits your design.
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The rules this checker applies
A quick reference for each geometric control under ASME Y14.5-2018, written in our own words. The standard itself is the authority; check it for the full conditions.
| Control | Datums | Ø zone | Ⓜ / Ⓛ on the tolerance | Applies to |
|---|---|---|---|---|
| ⏤ Straightness | Never | Yes, for the axis of a cylindrical feature of size | Only on a feature of size | Line elements of a surface, or the axis / median line of a feature of size |
| ⏥ Flatness | Never | No | Only on a width feature of size (derived median plane) | A flat surface, or the median plane of a width feature |
| ○ Circularity | Never | No | Never | Cross-sections of cylinders, cones and spheres |
| ⌭ Cylindricity | Never | No | Never | A cylindrical surface |
| ⌒ ⌓ Profile | Optional (without datums it controls form only) | No | Never (datum references may use MMB) | Line elements or whole surfaces of any shape |
| ∠ ⟂ ∥ Orientation | Required | Yes, for the axis of a cylindrical feature of size | Only on a feature of size | A surface, an axis or a center plane |
| ⌖ Position | Normally required | Yes, for cylindrical features (not for slots or tabs) | Yes | Features of size only — use profile for surfaces |
| ↗ ⌰ Runout | Required (a datum axis) | No | Never; datums are regardless of size | Surfaces around a datum axis |
| ◎ Concentricity, ⌯ Symmetry | Removed in Y14.5-2018. Under 2009: datums required, regardless of feature size only. Use position, runout or profile instead. | |||
Common frame mistakes
- Zero tolerance with no modifier. Nothing can be made or inspected to zero. Zero is legal only at MMC or LMC on a feature of size, where the tolerance comes from bonus.
- Datums on flatness. Flatness controls form only. If the face has to sit relative to something, use parallelism, perpendicularity or profile.
- Ⓜ on a flat face. A flat face has no size, so a material condition means nothing there.
- Position on a surface. Position locates features of size. A surface is located with profile.
- Concentricity or symmetry on a 2018 drawing. Both symbols were removed. The drawing must change the symbol or the edition it cites.
- Datum letters I, O and Q. They read as 1 and 0, so they are not used.