Shaft and Hole Clearance Fit Limits Calculator
Given the hole and shaft deviations, this tool returns the clearance range of the assembly and classifies the fit. It works for any combination, not only the standard H7/g6 pairs, so you can test custom limits before releasing a drawing.
Your numbers
Basic size, shared by hole and shaft. Used only for context in the notes.
Signed deviation of the hole minimum from nominal. H holes have 0.
Signed deviation of the hole maximum from nominal. H7 on 25 mm is +21 um.
Signed deviation of the shaft maximum from nominal. g6 on 25 mm is -7 um.
Signed deviation of the shaft minimum from nominal. g6 on 25 mm is -20 um.
Your results
Use the deviations from your drawing or from ISO 286-2 tables for the exact nominal size range. Shape errors, surface finish and temperature are not included.
Clearance limits vs hole upper deviation (um)
Sweeps Hole upper deviation (ES) from 5 to 80, holding your other inputs fixed.
Check fits across your item master
Optional: a walkthrough of how to run fit checks on drawing data held in your PLM or ERP.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the four deviations in micrometres with their signs. A hole usually has a lower deviation of zero (H class) and a positive upper deviation. A shaft below nominal has negative deviations. The calculator subtracts the shaft limits from the hole limits to get the smallest and largest gap. The chart sweeps the hole upper deviation so you can see how much a looser hole tolerance widens the maximum clearance, which is what drives rattle, leakage and bearing play.
The method
Minimum clearance is the hole at its smallest minus the shaft at its largest. Maximum clearance is the hole at its largest minus the shaft at its smallest. If the minimum is zero or positive the fit is a clearance fit. If the maximum is zero or negative every assembly is interference. Anything in between is a transition fit where some pairs clear and some interfere. The width of the range always equals the sum of the two tolerances, so tightening either part tightens the fit by the same amount.
- Clearance = hole size minus shaft size
- Negative values mean interference
- Fit tolerance = hole tolerance + shaft tolerance
- Worked check: H7/g6 on 25 mm gives 7 um to 41 um clearance
Mistakes to avoid
People often mix up signs for shaft deviations, so a shaft with es of -7 and ei of -20 is smaller than nominal. Another error is using the nominal size band wrongly when copying tolerance table values, since standard deviations change at each size step. Remember that this is a worst case calculation: a statistical assessment will show most assemblies far from the extremes. Also check temperature, coating thickness and surface roughness for running fits, since a plated or heavily finished shaft reduces the real clearance.
Frequently Asked Questions
What is the difference between clearance, transition and interference fits?
A clearance fit always leaves a gap, an interference fit always has the shaft larger than the hole, and a transition fit can produce either depending on the actual parts. The sign of the minimum and maximum clearance tells you which one applies.
Which deviations do I use for an H7 hole?
An H hole has a lower deviation of zero and an upper deviation equal to the IT7 tolerance for that size range, for example +21 um on 25 mm. Check ISO 286 tables for the size range, since the grade value changes by step.
Does this include thermal or surface effects?
No. It uses size limits only. Temperature differences, plating, burrs and roughness peaks reduce real clearance, so add allowances for running fits or for assemblies that operate at a temperature far from 20 C.
Why is the fit tolerance equal to the sum of both tolerances?
The largest gap uses the largest hole and smallest shaft and the smallest gap uses the reverse. Subtracting them leaves the hole tolerance plus the shaft tolerance, so the variation of the fit is purely additive.
If fit data sits in your PLM or ERP item master and you want it checked automatically, Netray can build a read-only check over your own data.
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