---
type: "gdt-symbol"
name: "Straightness"
symbol: "⏤"
unicode: "U+23E4"
unicode_name: "STRAIGHTNESS"
category: "form"
category_name: "Form controls"
datum_required: "never"
tolerance_zone: "Two parallel lines (surface element) or a cylinder (axis)"
aliases: ["straightness gdt", "line straightness", "axis straightness"]
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt/straightness
---

# Straightness (⏤) — GD&T Symbol, Tolerance Zone and Datum Rules

Limits how much a line element of a surface, or a feature's derived axis, may bend away from a perfect straight line. Applied to a surface it controls one line element at a time and takes no datum; applied to a feature of size with a diameter symbol it controls the derived median line and can carry a material-condition modifier.

- **Symbol**: ⏤ (Unicode U+23E4)
- **Category**: Form controls
- **Tolerance zone**: Two parallel lines (surface element) or a cylinder (axis)
- **Datum reference**: never references a datum
- **Standard**: ASME Y14.5 (cited, not reproduced); ISO 1101

## Straightness at a Glance

| Property | Value |
| --- | --- |
| Characteristic | Straightness |
| Symbol | ⏤ |
| Unicode codepoint | U+23E4 |
| Unicode name | STRAIGHTNESS |
| Category | Form controls |
| Tolerance zone | Two parallel lines (surface element) or a cylinder (axis) |
| Datum reference | never references a datum |
| Standard | ASME Y14.5 (cited, not reproduced); ISO 1101 |

## How Straightness Behaves

Straightness belongs to the form controls group. Control the shape of a single feature against itself. Never reference a datum.

## Other Form controls Controls

The controls in the same category — the ones a drawing is choosing between when it specifies straightness.

| Control | Symbol | Tolerance zone or effect | Datum |
| --- | --- | --- | --- |
| [Flatness](https://shopmath.org/gdt/flatness.md) | ⏥ | Two parallel planes | never references a datum |
| [Circularity](https://shopmath.org/gdt/circularity.md) | ○ | Two concentric circles in each cross-section | never references a datum |
| [Cylindricity](https://shopmath.org/gdt/cylindricity.md) | ⌭ | Two coaxial cylinders | never references a datum |

## Sources and Method for Straightness

### Straightness definition

- **Source**: Symbols and codepoints: Unicode Character Database (Unicode License v3). Characteristic list cross-checked against NASA MSFC GD&T Basics (public domain). Descriptions written from scratch; no ASME Y14.5 text reproduced.
- **Method**: compiled
- **Verified against**: Unicode Character Database codepoint check; 98/98 structural checks passed

### 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; a drawing may render the same characteristic with a different font.
- 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

## Common Questions About Straightness in GD&T

### What does Straightness mean in GD&T?

Limits how much a line element of a surface, or a feature's derived axis, may bend away from a perfect straight line. Applied to a surface it controls one line element at a time and takes no datum; applied to a feature of size with a diameter symbol it controls the derived median line and can carry a material-condition modifier.

### What is the GD&T symbol for straightness?

Straightness uses the ⏤ symbol — Unicode U+23E4 (STRAIGHTNESS). It sits in the first compartment of the feature control frame.

### Does Straightness need a datum?

Straightness never references a datum. The tolerance zone floats to best-fit the feature, so there is nothing to reference it to.

### What is the tolerance zone for Straightness in GD&T?

The straightness tolerance zone is: Two parallel lines (surface element) or a cylinder (axis).

## Related pages

- Next control: [Flatness](https://shopmath.org/gdt/flatness.md) (⏥)
- All symbols: [GD&T symbol reference](https://shopmath.org/gdt.md)
- Tolerances: [ISO 286 fit reference](https://shopmath.org/fits.md)

---

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