Geometric Tolerance Symbols (GD&T)
Look up the meaning of the 14 geometric-tolerance (GD&T) symbols and see which require a datum. GD&T controls a part's form, orientation and location — complementing dimensional tolerances so drawings are unambiguous and inspection is consistent.
Form — no datum| Symbol | Characteristic | Datum | Controls |
|---|
| ⏤ | Straightness | No | Deviation of a line or axis from a perfect straight line. |
| ⏥ | Flatness | No | Deviation of a surface from a perfect plane. |
| ○ | Roundness | No | Deviation of a cross-section from a perfect circle. |
| ⌭ | Cylindricity | No | Combines roundness, straightness and taper of the whole cylinder. |
Profile| Symbol | Characteristic | Datum | Controls |
|---|
| ⌒ | Profile of a line | Optional | Deviation of a line profile from its theoretical form. |
| ⌓ | Profile of a surface | Optional | Deviation of a surface profile from its theoretical form. |
Orientation — datum required| Symbol | Characteristic | Datum | Controls |
|---|
| ∥ | Parallelism | Yes | Keeps the feature parallel to the datum. |
| ⊥ | Perpendicularity | Yes | Keeps the feature at 90° to the datum. |
| ∠ | Angularity | Yes | Keeps the feature at a specified angle to the datum. |
Location — datum required| Symbol | Characteristic | Datum | Controls |
|---|
| ⌖ | Position | Yes | True position of a center, axis or plane relative to the theoretically exact location (TED). |
| ◎ | Concentricity / coaxiality | Yes | The feature axis coincides with the datum axis. |
| ⌯ | Symmetry | Yes | The median plane of the feature is symmetric about the datum. |
Runout — datum required| Symbol | Characteristic | Datum | Controls |
|---|
| ↗ | Circular runout | Yes | Deviation of each individual cross-section as the part rotates about the datum axis. |
| ⌰ | Total runout | Yes | Deviation of the entire surface as the part rotates about the datum axis. |
Symbols render in the device font; if a glyph is missing, read the characteristic column. “Datum” = whether the characteristic references a datum: No (form), Yes (orientation/location/runout), Optional (profile — with or without a datum). Actual tolerance values and theoretically exact dimensions (TED) come from the drawing; this table only explains the symbols.
Frequently asked questions
How many GD&T symbols are there?
14 symbols per ISO 1101 / JIS B 0021, in five groups: form, profile, orientation, location and runout.
Which characteristics need a datum?
Orientation, location and runout need a datum; form characteristics (straightness, flatness, roundness, cylindricity) do not. See the datum note column in the table.
How is GD&T different from dimensional tolerance?
Dimensional tolerance limits size; GD&T limits form, orientation and location. The two complement each other on the same drawing.
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