---
type: "gdt-symbol"
name: "Concentricity"
symbol: "◎"
unicode: "U+25CE"
category: "location"
category_name: "Location controls"
datum_required: "always"
tolerance_zone: "A cylinder centred on the datum axis, applied to derived median points"
aliases: ["concentricity gdt", "concentricity vs runout"]
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt/concentricity
---

# Concentricity (◎) — GD&T Symbol, Tolerance Zone and Datum Rules

Constrains the derived median points of a feature to a cylindrical zone about a datum axis. It is expensive to inspect because it requires deriving opposed-point midpoints rather than probing a surface, so runout or position is usually the better choice; ASME Y14.5-2018 removed it from the standard for exactly that reason.

- **Symbol**: ◎ (Unicode U+25CE)
- **Category**: Location controls
- **Tolerance zone**: A cylinder centred on the datum axis, applied to derived median points
- **Datum reference**: always references at least one datum
- **Standard**: ASME Y14.5 (cited, not reproduced); ISO 1101

## Concentricity at a Glance

| Property | Value |
| --- | --- |
| Characteristic | Concentricity |
| Symbol | ◎ |
| Unicode codepoint | U+25CE |
| Category | Location controls |
| Tolerance zone | A cylinder centred on the datum axis, applied to derived median points |
| Datum reference | always references at least one datum |
| Standard | ASME Y14.5 (cited, not reproduced); ISO 1101 |

## How Concentricity Behaves

Concentricity belongs to the location controls group. Control where a feature sits relative to a datum reference frame.

## Other Location controls Controls

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

| Control | Symbol | Tolerance zone or effect | Datum |
| --- | --- | --- | --- |
| [Position](https://shopmath.org/gdt/position.md) | ⌖ | A cylinder (or two parallel planes) centred on the true position | always references at least one datum |
| [Symmetry](https://shopmath.org/gdt/symmetry.md) | ⌯ | Two parallel planes centred on the datum centre plane | always references at least one datum |

## Sources and Method for Concentricity

### Concentricity 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 Concentricity in GD&T

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

Constrains the derived median points of a feature to a cylindrical zone about a datum axis. It is expensive to inspect because it requires deriving opposed-point midpoints rather than probing a surface, so runout or position is usually the better choice; ASME Y14.5-2018 removed it from the standard for exactly that reason.

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

Concentricity uses the ◎ symbol — Unicode U+25CE. It sits in the first compartment of the feature control frame.

### Does Concentricity need a datum?

Concentricity always references at least one datum. Without a datum reference frame the control has no origin to measure from.

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

The concentricity tolerance zone is: A cylinder centred on the datum axis, applied to derived median points.

## Related pages

- Previous control: [Position](https://shopmath.org/gdt/position.md) (⌖)
- Next control: [Symmetry](https://shopmath.org/gdt/symmetry.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/concentricity) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*