A clearance fit always provides a positive clearance between the hole and shaft. The maximum size of the shaft is always smaller than the minimum size of the hole. Used for bearings, sliding components, and free-running assemblies.
| Fit | Description | Typical Applications |
|---|---|---|
| H7/h6 | Locational clearance (very small gap) | Accurate locating, spigots |
| H7/g6 | Small clearance fit | Precision rotating shafts, linkages |
| H7/f7 | Moderate clearance | Running and sliding fits, journal bearings |
| H8/f7 | Larger running clearance | General rotating assemblies |
A transition fit may result in either a small clearance or a small interference depending on the actual manufacturing limits of the mating parts. Used for accurate location where slight tapping may be required for assembly.
| Fit | Description | Typical Applications |
|---|---|---|
| H7/js6 | Near-zero transition fit | Accurate positioning, hand assembly |
| H7/k6 | Light transition/interference | Hubs, accurate machine tool assemblies |
| H7/m6 | Tighter transition fit | Locating components, driven fits |
Produces a negative clearance (interference), meaning the shaft is intentionally manufactured larger than the hole. Assembly usually requires thermal expansion (heating the hole) or significant hydraulic pressing force.
| Fit | Description | Typical Applications |
|---|---|---|
| H7/p6 | Light interference fit | Permanent or semi-permanent, pressed bushes |
| H7/s6 | Medium interference | Gears, hubs, rigid couplings |
| H7/u6 | Heavy interference | High-load permanent assemblies, shrink fits |
The IT (International Tolerance) grade determines the width of the tolerance zone. Lower IT numbers represent tighter, more expensive manufacturing tolerances, while higher numbers represent wider, economical tolerances.
| Grade | Relative Precision | Typical Manufacturing Process |
|---|---|---|
| IT1 - IT4 | Ultra / Very High Precision | Lapping, honing, ultra-precision grinding |
| IT5 - IT7 | Precision | Grinding, fine broaching, precision turning |
| IT8 - IT9 | General Engineering | Turning, milling, reaming, boring |
| IT10 - IT11 | Medium Tolerance | Drilling, rough turning, milling |
| IT12 - IT16 | Coarse / Very Coarse | Casting, forging, flame cutting |
In a Hole-Basis system, the hole's lower deviation is zero (H), and fits are achieved by altering the shaft. In a Shaft-Basis system, the shaft's upper deviation is zero (h). Hole-basis is generally preferred because holes are harder to manufacture to custom sizes than shafts.
| System | Zero Reference | Example Fits |
|---|---|---|
| Hole-Basis (H) | Hole minimum limit is exact nominal | H7/g6, H7/p6 |
| Shaft-Basis (h) | Shaft maximum limit is exact nominal | G7/h6, P7/h6 |