Which statement about a basic dimension is accurate?

Which statement about a basic dimension is accurate?

• A. It is an exact size or location dimension used to locate features within a true position tolerance and carries no tolerance.
• B. It is a nominal dimension bearing a tolerance.
• C. It defines the datum reference frame.
• D. It specifies the surface finish.

Answer: (A)

Basic dimensions are exact values used to define the intended location or size of features without attaching a tolerance to that dimension itself. They establish the target geometry that must be achieved relative to the datum reference frame, but the allowable variation around that target is provided by the geometric tolerance in the feature control frame, such as the true position tolerance. Because the basic dimension is considered exact, it carries no tolerance; any deviation from it is governed by the positional tolerance against datums, not by the basic dimension itself. This is why the statement is the best fit: it correctly describes basic dimensions as precise targets used to locate features within a true position tolerance, with no tolerance on the dimension itself. Basic dimensions do not define the datum reference frame—that’s set by the datums—and they do not specify surface finish.

Basic dimensions are exact values used to define the intended location or size of features without attaching a tolerance to that dimension itself. They establish the target geometry that must be achieved relative to the datum reference frame, but the allowable variation around that target is provided by the geometric tolerance in the feature control frame, such as the true position tolerance. Because the basic dimension is considered exact, it carries no tolerance; any deviation from it is governed by the positional tolerance against datums, not by the basic dimension itself. This is why the statement is the best fit: it correctly describes basic dimensions as precise targets used to locate features within a true position tolerance, with no tolerance on the dimension itself. Basic dimensions do not define the datum reference frame—that’s set by the datums—and they do not specify surface finish.