Which statement best describes flatness in GD&T?

Which statement best describes flatness in GD&T?

• A. A form tolerance controlling how much a surface deviates from a true plane.
• B. A form tolerance describing curvature of a surface.
• C. A size tolerance controlling the thickness of a feature.
• D. A positional tolerance for locating features on a surface.

Answer: (B)

Flatness is a form tolerance that defines how much a surface can deviate from a true plane. The tolerance zone is a pair of parallel planes, and the entire surface must lie between them. This focuses on the surface shape itself, not its size, orientation relative to other features, or any curvature along the surface. Because it constrains deviation from planarity, flatness does not describe curvature of the surface. The other ideas—controlling thickness as a size tolerance or locating features with a positional tolerance—are separate concepts that deal with different geometric aspects.

Flatness is a form tolerance that defines how much a surface can deviate from a true plane. The tolerance zone is a pair of parallel planes, and the entire surface must lie between them. This focuses on the surface shape itself, not its size, orientation relative to other features, or any curvature along the surface. Because it constrains deviation from planarity, flatness does not describe curvature of the surface. The other ideas—controlling thickness as a size tolerance or locating features with a positional tolerance—are separate concepts that deal with different geometric aspects.