GD&T Reference→Location→Symmetry

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SYMMETRY

LOCATION

Controls median points of a feature relative to a datum plane

⚠ DATUM REQUIREDASME Y14.5-2009 §7.7 (removed in 2018)

Symmetry controls all median points of a feature relative to a datum center plane. All midpoints of the feature must lie within two parallel planes centered on the datum. Like concentricity, symmetry was removed from ASME Y14.5-2018 — use position instead.

WHEN TO USE IT

Symmetry was used to ensure a feature is centered relative to a datum plane. Per ASME Y14.5-2018, use position with a center plane datum to achieve the same result. Only use symmetry when working to ASME Y14.5-2009 or earlier.

COMMON MISTAKES

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Using symmetry on a 2018-compliant drawing — it was removed from the 2018 standard

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Omitting the datum reference — symmetry always requires a datum center plane

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Using symmetry when position would better serve the requirement

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Confusing symmetry with concentricity — symmetry applies to non-circular features

IS YOUR CALLOUT CORRECT?

Check these before releasing your drawing.

Is the drawing governed by ASME Y14.5-2009 or earlier?

Symmetry was removed in 2018. Use position for current drawings.

Does the FCF include a datum center plane reference?

Symmetry always requires a datum center plane.

Would position with a center plane datum serve the same function?

Position is preferred in the 2018 standard and is easier to inspect.

RELATED SYMBOLS

OTHER LOCATION CONTROLS

⊕Position ◎Concentricity

Redprint checks symmetry automatically

Redprint flags symmetry callouts on drawings referencing ASME Y14.5-2018, since symmetry was removed from that standard.

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