A fit designation compresses two separate size intervals into a few characters. Before deciding what it means for an assembly, expand the hole and shaft limits and compare their extremes. A nominal diameter alone does not specify the manufactured sizes.
Start with the diameter band
For an 8 mm nominal diameter, the reference band is over 6 mm through 10 mm, including its upper endpoint. The uppercase H8 describes a hole; lowercase g6 describes a shaft. The letter locates the tolerance zone relative to nominal, and the number selects its width. The supplied reference gives H8 deviations of 0 to +22 µm and g6 deviations of −14 to −5 µm in this band.
These are the values used in our fits and tolerances calculator, based on the Güvenal hole and shaft chart and cross-checked against MISUMI’s fit reference. Use the chart’s diameter band, not the physically closest printed row.
Convert before subtracting
Limit (mm) = nominal (mm) + deviation (µm) / 1000Cmin = smallest hole − largest shaftCmax = largest hole − smallest shaft| Feature | Minimum, mm | Maximum, mm |
|---|---|---|
| Hole H8 | 8.000 | 8.022 |
| Shaft g6 | 7.986 | 7.995 |
The smallest clearance is 8.000 − 7.995 = 0.005 mm. The largest is 8.022 − 7.986 = 0.036 mm. Every size combination inside these intervals has positive dimensional clearance. These are diameter differences: radial clearance for concentric ideal cylinders is half of each value.
Read the sign, then review the application
If the entire clearance interval is negative, the shaft is larger than the hole and the result is interference. An interval spanning negative and positive values is a transition fit. A zero endpoint permits exact dimensional contact; it should remain visible in the result instead of being rounded into a reassuring positive gap.
A dimensional result does not account for temperature, surface texture, roundness, coatings, lubrication, elastic deformation or service loads. Likewise, a measured part inside the stated size interval is not automatically a conformity decision: instrument uncertainty and the agreed decision rule still matter.
Use the bounded reference deliberately
The tool’s class lookup covers 3 < diameter ≤ 120 mm and its listed classes only. Outside that scope, enter reviewed drawing limits manually. Do not extrapolate a neighboring class or treat M8 here as a metric thread callout. Before releasing production dimensions, verify the result against the controlled drawing and applicable current standard; this worked example is not a standards-compliance certificate.
Calculate the example in Fits & Tolerances ↗