Metrology — Define “Tolerance” in Limits and Fits For a given dimension, what do we call the difference between the specified upper limit size and lower limit size?

Introduction / Context:
Limits and fits ensure interchangeability by controlling size variations. Designers and inspectors must use precise terms—mixing up tolerance, allowance, and size definitions leads to errors in drawings and inspection reports.

Given Data / Assumptions:

• Dimension has an upper limit and a lower limit on an engineering drawing.
• Measurements follow standard ISO/ANSI conventions.
• We are defining a term, not calculating a value.

Concept / Approach:
Tolerance is the permitted size variation, defined as upper limit minus lower limit. Allowance, in contrast, is the intentional difference between mating parts’ basic sizes (e.g., minimum clearance or maximum interference). Nominal or basic size is the reference from which limits are derived; actual size is what is measured on the part produced.

Step-by-Step Solution:
Upper limit − Lower limit = permitted variation.By definition, this is called “tolerance”.Therefore, select option “tolerance”.

Verification / Alternative check:
Standards glossaries (ISO 286) define tolerance exactly as the difference between the limits of size.

Why Other Options Are Wrong:
Nominal/basic size: reference dimensions, not a range.Actual size: the measured value on the finished part.Allowance: intended fit difference between mating components, not a single-part variation.

Common Pitfalls:
Interchanging allowance and tolerance; one is for mating parts, the other for permissible size variation.

Final Answer:
tolerance