Standards vocabulary: what do we call the theoretically exact size from which the limits of size (upper and lower permissible values) are established for a feature?

Introduction / Context:
Limits and fits systems are built around a reference size. This reference is not a measured value but a theoretically exact starting point used to derive permissible variation.

Given Data / Assumptions:

• A feature has an upper and lower limit of size.
• Those limits are derived from a common reference value.
• We need the standard term for that reference.

Concept / Approach:
“Basic size” is the theoretically exact value from which tolerances are applied to produce limits. It underlies hole-basis or shaft-basis fits and is fundamental to tolerance charting.

Step-by-Step Solution:

Verification / Alternative check:
Review standards tables (e.g., ISO fits): basic size is the column heading from which tolerances are applied to obtain limits.

Why Other Options Are Wrong:

• Actual Size: measured value on the produced part.
• Dimensioned size: the printed nominal; may equal the basic but not necessarily emphasized as theoretical reference.
• Production size: not a standard term.

Common Pitfalls:
Assuming “dimensioned size” and “basic size” are always identical; in GD&T contexts, “basic” may appear boxed to denote theoretically exact dimensions (for locations or profiles), which is distinct from limits-of-size basics.

Final Answer:
Basic size