---
type: "hub"
name: "GD&T symbol reference"
characteristic_count: 14
modifier_count: 8
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt
---

# GD&T Symbols — Geometric Characteristics, Zones and Datum Rules

The 14 geometric characteristics of ASME Y14.5 and ISO 1101, plus 8 modifiers, each with its symbol, Unicode codepoint, tolerance zone and whether it references a datum. Every description is original prose written against the standards, not reproduced from them.

## Control Categories

| Category | Controls | What it does |
| --- | --- | --- |
| Form controls | 4 | Control the shape of a single feature against itself. Never reference a datum. |
| Orientation controls | 3 | Control the angle of a feature relative to a datum, but not its distance. |
| Location controls | 3 | Control where a feature sits relative to a datum reference frame. |
| Modifiers and material conditions | 8 | Change how a geometric tolerance is interpreted or verified. |

_A category appears here only when it carries at least three controls._

## Geometric Characteristics

| Control | Symbol | Category | Tolerance zone | Datum required |
| --- | --- | --- | --- | --- |
| [Straightness](https://shopmath.org/gdt/straightness.md) | ⏤ | Form | Two parallel lines (surface element) or a cylinder (axis) | never |
| [Flatness](https://shopmath.org/gdt/flatness.md) | ⏥ | Form | Two parallel planes | never |
| [Circularity](https://shopmath.org/gdt/circularity.md) | ○ | Form | Two concentric circles in each cross-section | never |
| [Cylindricity](https://shopmath.org/gdt/cylindricity.md) | ⌭ | Form | Two coaxial cylinders | never |
| [Profile of a Line](https://shopmath.org/gdt/profile-of-a-line.md) | ⌒ | Profile | Two curves offset from the true profile, in each cross-section | sometimes |
| [Profile of a Surface](https://shopmath.org/gdt/profile-of-a-surface.md) | ⌓ | Profile | Two surfaces offset from the true profile | sometimes |
| [Angularity](https://shopmath.org/gdt/angularity.md) | ∠ | Orientation | Two parallel planes (or a cylinder, for an axis) at the basic angle | always |
| [Perpendicularity](https://shopmath.org/gdt/perpendicularity.md) | ⟂ | Orientation | Two parallel planes (or a cylinder, for an axis) normal to the datum | always |
| [Parallelism](https://shopmath.org/gdt/parallelism.md) | ∥ | Orientation | Two parallel planes (or a cylinder, for an axis) parallel to the datum | always |
| [Position](https://shopmath.org/gdt/position.md) | ⌖ | Location | A cylinder (or two parallel planes) centred on the true position | always |
| [Concentricity](https://shopmath.org/gdt/concentricity.md) | ◎ | Location | A cylinder centred on the datum axis, applied to derived median points | always |
| [Symmetry](https://shopmath.org/gdt/symmetry.md) | ⌯ | Location | Two parallel planes centred on the datum centre plane | always |
| [Circular Runout](https://shopmath.org/gdt/circular-runout.md) | ↗ | Runout | Full indicator movement in each single cross-section | always |
| [Total Runout](https://shopmath.org/gdt/total-runout.md) | ⌰ | Runout | Full indicator movement across the whole surface | always |

## Modifiers and Material Conditions

Modifiers change how a geometric tolerance is interpreted or verified; they are not controls in their own right.

| Modifier | Symbol | Unicode | Effect |
| --- | --- | --- | --- |
| [Maximum Material Condition (MMC)](https://shopmath.org/gdt/maximum-material-condition.md) | Ⓜ | U+24C2 | States that the stated tolerance applies when the feature contains the most material — the largest pin or the smallest hole. |
| [Least Material Condition (LMC)](https://shopmath.org/gdt/least-material-condition.md) | Ⓛ | U+24C1 | The mirror of MMC: the stated tolerance applies when the feature contains the least material — the smallest pin or the largest hole. |
| [Regardless of Feature Size (RFS)](https://shopmath.org/gdt/regardless-of-feature-size.md) | Ⓢ | U+24C8 | The default condition since 1994: the geometric tolerance applies at whatever size the feature is actually produced, with no bonus. |
| [Projected Tolerance Zone](https://shopmath.org/gdt/projected-tolerance-zone.md) | Ⓟ | U+24C5 | Zone projected above the feature |
| [Free State](https://shopmath.org/gdt/free-state.md) | Ⓕ | U+24BB | Says the requirement is to be verified with no restraining force applied. |
| [Tangent Plane](https://shopmath.org/gdt/tangent-plane.md) | Ⓣ | U+24C9 | Evaluates an orientation control against a plane resting on the high points of the surface rather than against every point of it. |
| [Unequally Disposed Profile](https://shopmath.org/gdt/unequally-disposed-profile.md) | Ⓤ | U+24CA | Profile band split unevenly about the true profile |
| [Diameter](https://shopmath.org/gdt/diameter.md) | ⌀ | U+2300 | Inside a feature control frame this makes the tolerance zone cylindrical rather than a pair of parallel planes. |

## Sources and Method for the GD&T Data

### GD&T geometric characteristics and modifiers

- **Source**: Unicode Character Database (Unicode License v3); characteristic list cross-checked against NASA MSFC GD&T Basics (public domain); descriptions written from scratch
- **Method**: compiled
- **Verified against**: gdt: 98 checks passed across 1 harness(es)

### Assumptions

- Descriptions are original prose. No ASME Y14.5 definitional text, worked example or figure is reproduced — the standard is cited, not copied.
- Symbol glyphs and codepoints are from the Unicode Character Database.
- Dataset scope: EXCLUDED: all ASME Y14.5 definitional text, worked examples and figures. Every description on this site is original prose.

**Data last verified**: August 1, 2026

## Related pages

- Tolerances and fits: [ISO 286 fit reference](https://shopmath.org/fits.md)
- Threads: [Screw thread reference](https://shopmath.org/threads.md)

---

*Source: [ShopMath](https://shopmath.org/gdt) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*