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A boxed letter on a filled or open triangle, establishing a reference.
Also known as: Datum symbol, Letter in a box on a triangle
A boxed letter on a triangle names a datum — the surface everything else is measured from. Choosing which face is datum A is a manufacturing decision as much as a drawing one, because it determines how the part is held.
Establishes a surface or feature as a datum, labelled with a letter that tolerance frames elsewhere on the drawing refer to.
Contexts: Technical drawing
Determines how the part is held for inspection and often for machining, so the choice of datum is a manufacturing decision rather than a purely graphical one.
Contexts: Technical drawing
A capital letter inside a small square box, joined by a short leader to a solid or open triangle resting on the surface it identifies.
Frames reference the datums these symbols establish.