---
type: "gdt-symbol"
name: "Parallelism"
symbol: "∥"
unicode: "U+2225"
unicode_name: "PARALLEL TO"
category: "orientation"
category_name: "Orientation controls"
datum_required: "always"
tolerance_zone: "Two parallel planes (or a cylinder, for an axis) parallel to the datum"
aliases: ["parallelism gdt", "flatness vs parallelism"]
standard: "ASME Y14.5 (cited, not reproduced); ISO 1101"
verified: "August 1, 2026"
url: https://shopmath.org/gdt/parallelism
---

# Parallelism (∥) — GD&T Symbol, Tolerance Zone and Datum Rules

Angularity's zero-degree special case. It limits how much a surface or axis may tilt relative to a datum, but places no limit on how far away it sits — distance is the job of the linear dimension or of a profile or position callout.

- **Symbol**: ∥ (Unicode U+2225)
- **Category**: Orientation controls
- **Tolerance zone**: Two parallel planes (or a cylinder, for an axis) parallel to the datum
- **Datum reference**: always references at least one datum
- **Standard**: ASME Y14.5 (cited, not reproduced); ISO 1101

## Parallelism at a Glance

| Property | Value |
| --- | --- |
| Characteristic | Parallelism |
| Symbol | ∥ |
| Unicode codepoint | U+2225 |
| Unicode name | PARALLEL TO |
| Category | Orientation controls |
| Tolerance zone | Two parallel planes (or a cylinder, for an axis) parallel to the datum |
| Datum reference | always references at least one datum |
| Standard | ASME Y14.5 (cited, not reproduced); ISO 1101 |

## How Parallelism Behaves

Parallelism belongs to the orientation controls group. Control the angle of a feature relative to a datum, but not its distance.

## Other Orientation controls Controls

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

| Control | Symbol | Tolerance zone or effect | Datum |
| --- | --- | --- | --- |
| [Angularity](https://shopmath.org/gdt/angularity.md) | ∠ | Two parallel planes (or a cylinder, for an axis) at the basic angle | always references at least one datum |
| [Perpendicularity](https://shopmath.org/gdt/perpendicularity.md) | ⟂ | Two parallel planes (or a cylinder, for an axis) normal to the datum | always references at least one datum |

## Sources and Method for Parallelism

### Parallelism 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 Parallelism in GD&T

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

Angularity's zero-degree special case. It limits how much a surface or axis may tilt relative to a datum, but places no limit on how far away it sits — distance is the job of the linear dimension or of a profile or position callout.

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

Parallelism uses the ∥ symbol — Unicode U+2225 (PARALLEL TO). It sits in the first compartment of the feature control frame.

### Does Parallelism need a datum?

Parallelism 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 Parallelism in GD&T?

The parallelism tolerance zone is: Two parallel planes (or a cylinder, for an axis) parallel to the datum.

## Related pages

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