What type of tolerances do basic dimensions define?

What type of tolerances do basic dimensions define?

• A. Toleranced dimensions with manufacturing allowances.
• B. Exact values used to locate features.
• C. Height and depth only.
• D. Material condition.

Answer: (B)

In GD&T, basic dimensions are exact, theoretically exact values that define the intended location or size of features. They do not carry a tolerance themselves; instead, they serve as the target values used by geometric tolerances to constrain variation. The actual allowable deviation comes from the geometric tolerance specified in the feature control frame, which governs how far a feature can be from the basic value while still being acceptable. This setup lets you specify precise relationships—such as true position or true profile—independent of manufacturing variation, with the tolerances indicating how much deviation is allowed from those exact targets. Basic dimensions are not about manufacturing allowances, nor are they limited to height or depth, and they are distinct from material-condition limits like MMC or LMC.

In GD&T, basic dimensions are exact, theoretically exact values that define the intended location or size of features. They do not carry a tolerance themselves; instead, they serve as the target values used by geometric tolerances to constrain variation. The actual allowable deviation comes from the geometric tolerance specified in the feature control frame, which governs how far a feature can be from the basic value while still being acceptable. This setup lets you specify precise relationships—such as true position or true profile—independent of manufacturing variation, with the tolerances indicating how much deviation is allowed from those exact targets. Basic dimensions are not about manufacturing allowances, nor are they limited to height or depth, and they are distinct from material-condition limits like MMC or LMC.