Limits and fits — meaning of a unilateral tolerance system In a unilateral system of tolerance specification, the dimensional tolerance zone is permitted on which side(s) of the nominal size?

Introduction / Context:
Tolerancing determines how far a manufactured part may deviate from the nominal size and still function. Understanding unilateral versus bilateral tolerance placement is essential for selecting gauges, planning machining operations, and ensuring fit interchangeability.

Given Data / Assumptions:

• Nominal (basic) size is specified on the drawing.
• We compare where the permissible variation lies relative to this nominal size.
• “Actual size” is the measured size after manufacture, not the reference for assigning limits.

Concept / Approach:
In a unilateral tolerance system, the entire tolerance zone lies on one side of the nominal size. For example, 50.00 mm +0.00/−0.10 mm places all variation below the nominal. By contrast, a bilateral tolerance splits variation on both sides (e.g., 50.00 ± 0.05 mm). The key phrase is “relative to nominal size,” not “relative to actual size,” which varies from part to part and is not a datum for specification.

Step-by-Step Solution:

Verification / Alternative check:
Standards for limits and fits (e.g., ISO system) illustrate unilateral zones such as H7 (holes) where lower deviation is zero and upper deviation is positive, fully on one side of basic size.

Why Other Options Are Wrong:

• “One/both sides of actual size”: the actual size is an outcome, not the specification reference.
• “Both sides of nominal size”: that defines a bilateral tolerance.
• “Neither side”: incorrect; a tolerance zone must exist for manufacture.

Common Pitfalls:
Confusing unilateral with “limit” dimensions; misinterpreting gauge descriptions like GO at basic size for certain fits.

Final Answer: