What is the appearance of the flatness symbol?

• A. A circle
• B. A parallelogram
• C. A triangle
• D. A square

Answer: (B)

The flatness symbol in Geometric Dimensioning and Tolerancing (GD&T) is represented by a parallelogram. This symbol indicates that a surface must be flat within a specified tolerance. The parallelogram shape signifies a two-dimensional condition where the surfaces must be controlled for flatness.

In GD&T, flatness control requires that every point on a specified surface falls within two parallel planes, which are a certain distance apart, corresponding to the tolerance defined. This tolerance ensures that the surface is uniform and does not have any deviations that could affect the proper functioning of the parts in assembly.

Choosing the parallelogram correctly conveys the idea that flatness is a geometric condition applied to a planar surface, setting it apart from the other options, which do not denote flatness in GD&T terms.