Machining
ISO tolerances handbook online
Pick an IT grade and limit deviations for a shaft or hole by nominal size. Useful when designing fits and preparing drawings.
Tolerance reference (IT grades)
Tolerances per ISO 286 from nominal size range tables. T is constant within a size range (µm). The result gives limit dimensions in the hole-basis (H) and shaft-basis (h) systems.
Nominal size range
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Tolerance T
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IT5–IT7 — high-precision fits. IT8–IT11 — general mechanical engineering. IT12–IT16 — free dimensions and blanks.
Frequently asked questions
What does an IT tolerance grade mean?
IT (International Tolerance) is the ISO 286 accuracy series. A smaller IT number means a tighter tolerance and higher machining precision.
How do I choose a shaft–hole fit?
Decide the fit type (clearance, interference or transition), then pick nominal size and IT for shaft and hole. The handbook shows limit deviations for the size range.