Introduction / Context:
Designers frequently use standardized fit systems to specify how holes and shafts mate. The ISO system provides a comprehensive metric framework using tolerance grades (IT) and fundamental deviations (letters such as H, h) to define clearance, transition, and interference fits consistently across industries.
Given Data / Assumptions:
- Metric dimensions are used in the design.
- Fit class communicates intended functional relationship between mating parts.
- Suppliers and inspectors recognize ISO fit notation.
Concept / Approach:
The ISO system assigns standardized tolerance zones to holes and shafts. For example, H7/h6 indicates a commonly used clearance fit. Using standardized fits simplifies global communication, tooling selection, and quality verification by referencing established limits rather than ad hoc values.
Step-by-Step Solution:
Identify mating features (e.g., hole and shaft) and required functional fit.Select an ISO tolerance grade and deviation (e.g., H7/h6) that produces the desired allowance.Apply the callout on the drawing; derive limit sizes from the standard tables.Verify process capability to achieve the selected grades consistently.
Verification / Alternative check:
Compare against national standards; ISO fits align with widely adopted industry practice for metric systems.
Why Other Options Are Wrong:
Incorrect: ISO indeed maintains a metric fit system.Applies only to inch threads / Used only in automotive: The ISO system is metric and broadly applied, not limited to threads or one industry.
Common Pitfalls:
Mixing inch-based ANSI fits with metric ISO fits within one assembly, causing confusion.Choosing overly tight grades without necessity, increasing cost.
Final Answer:
Correct
Discussion & Comments