GD&T · Form · ASME Y14.5
Circularity GD&T Symbol — Meaning and Datum Rule
https://shopmath.org/gdt/circularity · data verified August 1, 2026
Circularity (○) is a GD&T form control, and its tolerance zone is two concentric circles in each cross-section. It never references a datum.
- Symbol
- ○
- Unicode
- U+25CB
- Category
- Form
- Datum
- never
Circularity · GD&T form symbol
○
- Unicode
- U+25CB
- Datum
- never
- Zone
- Two concentric circles in each cross-section
The value in the feature control frame is the width or diameter of that zone, in the drawing's units.
What Circularity Controls in GD&T
Checked one cross-section at a time: every point around the section must lie in the ring between two concentric circles whose radii differ by the tolerance value. Each section is judged independently, so circularity catches lobing and out-of-round but not taper or bend along the length.
The Circularity 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.
| Property | Value |
|---|---|
| Symbol | ○ |
| Unicode codepoint | U+25CB |
| Category | Form controls — Control the shape of a single feature against itself. Never reference a datum. |
| Tolerance zone | Two concentric circles in each cross-section |
| 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 | roundness, out of round |
The symbol character is the Unicode codepoint used in drawings and CAD annotations; drafting standards render it with defined proportions that the font approximates.
Sources and Method for the Circularity GD&T Reference
- Circularity 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 to Cite This Circularity GD&T Reference
Citation
ShopMath. "Circularity GD&T Symbol — Meaning and Datum Rule." ShopMath, verified August 1, 2026, https://shopmath.org/gdt/circularity
BibTeX
@misc{shopmath-gdt-circularity,
title = {Circularity GD&T Symbol — Meaning and Datum Rule},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/gdt/circularity}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/gdt/circularity
Common Questions About Circularity in GD&T
What does Circularity mean in GD&T?
- Checked one cross-section at a time: every point around the section must lie in the ring between two concentric circles whose radii differ by the tolerance value. Each section is judged independently, so circularity catches lobing and out-of-round but not taper or bend along the length.
What is the Circularity symbol in GD&T?
- ○ — Unicode U+25CB. It goes in the first compartment of the feature control frame, ahead of the tolerance value.
Does Circularity 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 Circularity tolerance zone?
- Two concentric circles in each cross-section. 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 Circularity?
- Circularity is one of 4 form controls: Circularity, Straightness, Flatness, Cylindricity.