Symmetry tolerance symbol

Three horizontal lines in a tolerance frame.

Also known as: Symmetry callout

Engineering & technicalStandard profile

Meanings

Symmetry limits how far a feature's median plane may stray from a datum plane. Like concentricity it is hard to inspect and was removed from ASME Y14.5 in 2018, though it remains in ISO practice.

Officially standardisedVerified fact
Limits the deviation of a feature's median plane from a datum plane.
Contexts: Technical drawing
Officially standardisedVerified fact
Was withdrawn from ASME Y14.5 in 2018 alongside concentricity for the same reason of inspection difficulty, and remains current in ISO practice.
Contexts: Technical drawing

Visual description

Three horizontal lines, the middle one longer, stacked in a rectangular frame.

Symmetry: horizontal
Orientation: upright

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

ISO 1101, Geometrical product specifications — Geometrical tolerancing
International Organization for Standardization · retrieved 2026-08-01
Paywalled and NOT READ. Registered so records can state which standard governs a symbol — a checkable fact a reader can act on — and for nothing else. It governs the geometric tolerancing symbols and their frames. No meaning in any record is typed `official` on the strength of this entry. See docs/paywalled-standards.md.
Geometric dimensioning and tolerancing
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.
ASME Y14.5, Dimensioning and Tolerancing
American Society of Mechanical Engineers · retrieved 2026-08-01
Paywalled and NOT READ. Registered so records can state which standard governs a symbol — a checkable fact a reader can act on — and for nothing else. It is the American counterpart to ISO 1101 and differs from it in detail. No meaning in any record is typed `official` on the strength of this entry. See docs/paywalled-standards.md.

Last reviewed 2026-08-23

Part of

Engineering drawing notation

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Meanings

Symmetry limits how far a feature's median plane may stray from a datum plane. Like concentricity it is hard to inspect and was removed from ASME Y14.5 in 2018, though it remains in ISO practice.

Officially standardisedVerified fact

Limits the deviation of a feature's median plane from a datum plane.

Contexts: Technical drawing

Officially standardisedVerified fact

Was withdrawn from ASME Y14.5 in 2018 alongside concentricity for the same reason of inspection difficulty, and remains current in ISO practice.

Contexts: Technical drawing

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

ISO 1101, Geometrical product specifications — Geometrical tolerancing
International Organization for Standardization · retrieved 2026-08-01
Paywalled and NOT READ. Registered so records can state which standard governs a symbol — a checkable fact a reader can act on — and for nothing else. It governs the geometric tolerancing symbols and their frames. No meaning in any record is typed `official` on the strength of this entry. See docs/paywalled-standards.md.
Geometric dimensioning and tolerancing
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.
ASME Y14.5, Dimensioning and Tolerancing
American Society of Mechanical Engineers · retrieved 2026-08-01
Paywalled and NOT READ. Registered so records can state which standard governs a symbol — a checkable fact a reader can act on — and for nothing else. It is the American counterpart to ISO 1101 and differs from it in detail. No meaning in any record is typed `official` on the strength of this entry. See docs/paywalled-standards.md.

Last reviewed 2026-08-23