What is the difference between 'profile of a line' and 'profile of a surface' in terms of control?

What is the difference between 'profile of a line' and 'profile of a surface' in terms of control?

• A. It controls a line contour.
• B. They both control the same thing.
• C. It controls only size of features.
• D. Profile of a line controls a line contour; profile of a surface controls an extended boundary.

Answer: (D)

In GD&T, the way a profile tolerance is applied depends on whether you’re addressing a line or a surface. A profile of a line constrains the contour along that line—the actual path of the line’s edge within a tolerance zone. It’s about how the line itself must appear when you trace it. A profile of a surface, by contrast, controls the extended boundary of the surface—the outline that defines the edge of the surface feature, across its entire length and curvature. So the difference in control is that the profile of a line governs the line contour, while the profile of a surface governs the entire extended boundary of the surface. The other options are incomplete or incorrect because they either ignore one of the boundaries, claim they control the same thing, or misstate that it only affects size.

In GD&T, the way a profile tolerance is applied depends on whether you’re addressing a line or a surface. A profile of a line constrains the contour along that line—the actual path of the line’s edge within a tolerance zone. It’s about how the line itself must appear when you trace it. A profile of a surface, by contrast, controls the extended boundary of the surface—the outline that defines the edge of the surface feature, across its entire length and curvature.

So the difference in control is that the profile of a line governs the line contour, while the profile of a surface governs the entire extended boundary of the surface. The other options are incomplete or incorrect because they either ignore one of the boundaries, claim they control the same thing, or misstate that it only affects size.