What is a basic dimension?

What is a basic dimension?

• A. An exact dimension used to locate features; it has no tolerance and is boxed.
• B. A dimension that indicates material condition.
• C. A dimension with allowable variation.
• D. A target dimension.

Answer: (A)

Basic dimensions are exact values used to define the true location or size relationship of features, with no tolerance attached. They are shown in a rectangular box on the drawing to signal that the dimension itself has no allowable variation; instead, any permissible deviation comes from the geometric tolerances applied to the features relative to these true values. This separation lets the designer specify precise placement or size targets while letting the manufacturing process control how far actual features can wander through a geometric tolerance zone. That’s why this choice is the best: it describes an exact dimension used to locate features, with no tolerance, and it is boxed to indicate that meaning. Other options describe material conditions or dimensions with tolerances, which are not the same as basic dimensions, or refer to terms like “target dimension” that aren’t standard GD&T for this concept.

Basic dimensions are exact values used to define the true location or size relationship of features, with no tolerance attached. They are shown in a rectangular box on the drawing to signal that the dimension itself has no allowable variation; instead, any permissible deviation comes from the geometric tolerances applied to the features relative to these true values. This separation lets the designer specify precise placement or size targets while letting the manufacturing process control how far actual features can wander through a geometric tolerance zone.

That’s why this choice is the best: it describes an exact dimension used to locate features, with no tolerance, and it is boxed to indicate that meaning. Other options describe material conditions or dimensions with tolerances, which are not the same as basic dimensions, or refer to terms like “target dimension” that aren’t standard GD&T for this concept.