ISO Fits Explained Simply
When this applies
Use this guide when you need shared vocabulary between design, machining, and inspection without opening a full standards course.
Tool to use
Browser-based preliminary check for ISO Fit Tolerance Helper — fast estimates, not code or stamped design output.
Open ISO Fit Tolerance Helper →Steps
- 1Choose hole-basis or shaft-basis preference consistent with your shop standards.
- 2Select a fit designation appropriate to motion vs permanence needs.
- 3Translate fit symbols into limit deviations for the chosen nominal.
- 4Verify manufacturing can hold the grades you specified.
- 5Document inspection criteria alongside functional intent.
Examples
- H7/g6-type discussions for sliding assemblies.
- Press-fit bearing seats requiring process-controlled interference.
What to avoid
- Specifying grades the shop cannot reliably measure.
- Confusing deviation sign conventions between shaft and hole.
- Skipping thermal and elastic deformation on critical press fits.
Related tools
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Browse all task guides or see the full list on the Engineering hub.
FAQ
Metric vs imperial fits?
Do not mix systems on the same drawing without explicit conversion notes.
Statistical tolerancing?
ISO fits assume traditional limit tolerancing unless you adopt statistical methods explicitly.