Dimensional control — definition of tolerance On a drawing, what do we call the total amount a feature is permitted to vary from the specified dimension?

Introduction / Context:
Tolerancing communicates acceptable variation so parts can be manufactured economically while still functioning in assemblies. Distinguishing between “tolerance,” “allowance,” and related terms is fundamental to successful design-for-manufacture and inspection planning.

Given Data / Assumptions:

• A nominal (basic) dimension is specified on the drawing.
• There is a permitted deviation above and/or below the nominal value.
• We are referring to the total permissible variation for a single feature.

Concept / Approach:
Tolerance is the total permissible variation from the specified dimension. It may be expressed as plus/minus values (e.g., 25.00 ± 0.10) or as limits (e.g., 24.90–25.10). Allowance, by contrast, is the intentional difference between mating parts' dimensions (e.g., minimum clearance or maximum interference) at the worst-case material limits.

Step-by-Step Solution:

Verification / Alternative check:
Standards texts (e.g., ASME Y14.5) define tolerance as permissible variation in size, form, or location, while allowance pertains to mating part relationships. Inspection procedures check conformance within tolerance limits.

Why Other Options Are Wrong:

• Allowance: deliberate difference between mating parts at MMC/LMC; not variation of a single dimension.
• Specification: the stated requirement itself, not the permitted variation.
• Difference: vague term without a standards definition.
• Clearance: positive space between mating parts, not the allowed dimensional spread.

Common Pitfalls:

• Confusing bilateral tolerances (±) with unilateral or limit tolerances; the total tolerance is the span between limits.

Final Answer:
Tolerance