What is a profile of a surface tolerance?

• A. A tolerance that defines the boundary for a single line boundary along its length.
• B. A tolerance that controls the flatness of a surface.
• C. A tolerance that confines the true form of a line boundary along its length.
• D. A tolerance that defines the allowable boundary for the entire surface, controlling its true shape in all directions.

Answer: (D)

Profile of a surface tolerance creates a 3D tolerance zone around the intended surface, so the actual surface must lie within that boundary everywhere. This controls the true shape of the surface in all directions, not just a single line or a single plane, ensuring the entire surface conforms to the designed form with respect to the datums.

This is different from flatness, which only constrains deviation from a perfectly flat plane, and from tolerances that describe a boundary for a line or a specific line boundary along its length. The essence of a profile of a surface is the overall form control of the entire surface.