What is the Straightness symbol in GD&T?

⏤ — Unicode U+23E4 (STRAIGHTNESS). It goes in the first compartment of the feature control frame, ahead of the tolerance value.

Does Straightness need a datum?

Never references a datum. The tolerance zone floats to best-fit the feature, so this control says nothing about where the feature sits relative to anything else.

What shape is the Straightness tolerance zone?

Two parallel lines (surface element) or a cylinder (axis). Every point of the controlled feature has to lie inside that zone for the part to pass.

Which GD&T controls are in the same group as Straightness?

Straightness is one of 4 form controls: Straightness, Flatness, Circularity, Cylindricity.

GD&T · Form · ASME Y14.5

Straightness GD&T Symbol — Meaning and Datum Rule

https://shopmath.org/gdt/straightness · data verified August 1, 2026

Straightness (⏤) is a GD&T form control, and its tolerance zone is two parallel lines (surface element) or a cylinder (axis). It never references a datum.

Symbol: ⏤
Unicode: U+23E4
Category: Form
Datum: never

Straightness · GD&T form symbol

⏤

Unicode: U+23E4
Datum: never
Zone: Two parallel lines (surface element) or a cylinder (axis)

The value in the feature control frame is the width or diameter of that zone, in the drawing's units.

What Straightness Controls 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.

The Straightness GD&T Symbol, Zone and Datum Rule

The symbol as it appears in the feature control frame, with the codepoint to type it and the rule it carries.

Straightness — GD&T symbol, tolerance zone and datum rule
Property	Value
Symbol	⏤
Unicode codepoint	U+23E4 (STRAIGHTNESS)
Category	Form controls — Control the shape of a single feature against itself. Never reference a datum.
Tolerance zone	Two parallel lines (surface element) or a cylinder (axis)
Datum reference	Never references a datum. The tolerance zone floats to best-fit the feature, so this control says nothing about where the feature sits relative to anything else.
Standard	ASME Y14.5 (cited, not reproduced); ISO 1101
Also called	line straightness, axis straightness

The symbol character is the Unicode codepoint used in drawings and CAD annotations; drafting standards render it with defined proportions that the font approximates.

GD&T Controls Related to Straightness

Straightness is a form control. Control the shape of a single feature against itself. Never reference a datum. These are the others in that group — the ones a drawing usually chooses between.

GD&T form symbols related to Straightness
Symbol	Datum	Tolerance zone
Flatness	never	Two parallel planes
Circularity	never	Two concentric circles in each cross-section
Cylindricity	never	Two coaxial cylinders

Ordered as they appear in the feature control frame reference, form through runout, then modifiers.

Sources and Method for the Straightness GD&T Reference

Straightness symbol and rulescompiled

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.

Verified against Unicode Character Database codepoint check; 98/98 structural checks passed

Compiled from independent public sources that agree cell-for-cell.

Assumptions

The standard is cited, never reproduced: no ASME Y14.5 definitional text, worked example or figure appears on this site. The description above is original prose.
ASME Y14.5 and ISO 1101 differ in places — the ISO system uses the envelope requirement differently and does not carry every ASME modifier. Where a drawing names a standard, that standard governs.
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

How this data is built and checked →

How to Cite This Straightness GD&T Reference

Citation

ShopMath. "Straightness GD&T Symbol — Meaning and Datum Rule." ShopMath, verified August 1, 2026, https://shopmath.org/gdt/straightness

BibTeX

@misc{shopmath-gdt-straightness,
  title        = {Straightness GD&T Symbol — Meaning and Datum Rule},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gdt/straightness}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gdt/straightness

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 Straightness symbol in GD&T?: ⏤ — Unicode U+23E4 (STRAIGHTNESS). It goes in the first compartment of the feature control frame, ahead of the tolerance value.
Does Straightness need a datum?: Never references a datum. The tolerance zone floats to best-fit the feature, so this control says nothing about where the feature sits relative to anything else.
What shape is the Straightness tolerance zone?: Two parallel lines (surface element) or a cylinder (axis). Every point of the controlled feature has to lie inside that zone for the part to pass.
Which GD&T controls are in the same group as Straightness?: Straightness is one of 4 form controls: Straightness, Flatness, Circularity, Cylindricity.

Every GD&T symbol and modifier