Which statement best describes the relationship between a basic dimension and a true position tolerance?

Which statement best describes the relationship between a basic dimension and a true position tolerance?

• A. A basic dimension indicates a size tolerance.
• B. A basic dimension provides exact target size/location; the true position tolerance defines allowable deviation from that target.
• C. A basic dimension is the tolerance zone itself.
• D. A true position tolerance is used to specify material condition.

Answer: (B)

Basic dimensions establish the exact target size or location of a feature, with no allowance for variation by themselves. The true position tolerance then defines how far the actual feature can deviate from that target location relative to datums, creating the allowable tolerance zone around the precise position. In other words, the basic dimension tells you where things should be, and the true position tolerance tells you how far the real part is allowed to wander from that location. For example, if a hole must be at an exact spot defined by basic dimensions, the true position tolerance specifies the cylindrical zone around that ideal spot within which the hole’s center must lie. The basic dimension does not itself provide a tolerance, and the tolerance zone comes from the true position specification, not from the basic dimension alone. The other options misstate the relationship: a basic dimension is not a size tolerance, and the tolerance zone is not the basic dimension itself. The true position tolerance is about locating features, not about specifying material condition, which involves different modifiers in GD&T.

Basic dimensions establish the exact target size or location of a feature, with no allowance for variation by themselves. The true position tolerance then defines how far the actual feature can deviate from that target location relative to datums, creating the allowable tolerance zone around the precise position. In other words, the basic dimension tells you where things should be, and the true position tolerance tells you how far the real part is allowed to wander from that location.

For example, if a hole must be at an exact spot defined by basic dimensions, the true position tolerance specifies the cylindrical zone around that ideal spot within which the hole’s center must lie. The basic dimension does not itself provide a tolerance, and the tolerance zone comes from the true position specification, not from the basic dimension alone.

The other options misstate the relationship: a basic dimension is not a size tolerance, and the tolerance zone is not the basic dimension itself. The true position tolerance is about locating features, not about specifying material condition, which involves different modifiers in GD&T.