Fitting tolerance controls how a spherical plain bearing is supported by the housing and pin. A fit that is too loose can permit movement outside the intended sliding surface; a fit that is too tight can distort the ring or make assembly unnecessarily difficult. H7 and h6 are useful reference classes, but they are not universal answers for every load case.
Reading ISO tolerance class names
The letter identifies the location of the tolerance zone relative to the nominal size, while the number identifies the tolerance grade. For the reference tables below, H bore classes have a zero lower deviation and a positive upper deviation. h shaft classes have a zero upper deviation and a negative lower deviation.
Metric bore tolerance reference
| Nominal diameter mm | H6 mm | H7 mm | H8 mm |
|---|---|---|---|
| 3-6 | 0 / +0.008 | 0 / +0.012 | 0 / +0.018 |
| 6-10 | 0 / +0.009 | 0 / +0.015 | 0 / +0.022 |
| 10-18 | 0 / +0.011 | 0 / +0.018 | 0 / +0.027 |
| 18-30 | 0 / +0.013 | 0 / +0.021 | 0 / +0.033 |
| 30-50 | 0 / +0.016 | 0 / +0.025 | 0 / +0.039 |
| 50-80 | 0 / +0.019 | 0 / +0.030 | 0 / +0.046 |
| 80-120 | 0 / +0.022 | 0 / +0.035 | 0 / +0.054 |
Metric shaft tolerance reference
| Nominal diameter mm | g6 mm | h6 mm | h7 mm |
|---|---|---|---|
| 3-6 | -0.004 / -0.012 | 0 / -0.008 | 0 / -0.012 |
| 6-10 | -0.005 / -0.014 | 0 / -0.009 | 0 / -0.015 |
| 10-18 | -0.006 / -0.017 | 0 / -0.011 | 0 / -0.018 |
| 18-30 | -0.007 / -0.020 | 0 / -0.013 | 0 / -0.021 |
| 30-50 | -0.009 / -0.025 | 0 / -0.016 | 0 / -0.025 |
| 50-80 | -0.010 / -0.029 | 0 / -0.019 | 0 / -0.030 |
| 80-120 | -0.012 / -0.034 | 0 / -0.022 | 0 / -0.035 |
What H7 / h6 means for a 20 mm joint
For the 18-30 mm range, the H7 bore reference shown on this site is 0 / +0.021 mm and the h6 shaft reference is 0 / -0.013 mm. These are useful values when reading a drawing or checking an existing interface, but the final fit still depends on ring loading, housing stiffness, temperature, surface condition and assembly method.
Fit decisions by series
A heavy-duty GEG joint, a pressed maintenance-free GE..C bearing and a conventional GE steel/steel bearing do not automatically deserve the same fit. Treat the tolerance table as a reference library, then apply the governing machine design or approved engineering fit for the actual configuration.
Installation implications
- Measure the housing bore and pin with appropriate metrology before assembly.
- Use a press or correctly sized driver so installation force is applied to the ring being fitted.
- Do not transmit installation force through the spherical sliding contact.
- After assembly, verify free articulation and the required axial/shoulder clearances.
Why housing stiffness matters
A tolerance class describes the machined size range; it does not describe how the housing behaves under load. A thin clevis eye can expand or ovalize around the bearing, while a thick machined block may remain much more stable. That is why two applications using the same bearing can require different engineering decisions even if both drawings begin with an H-class bore reference.
Why the pin condition matters just as much
The inner-ring bore may be dimensionally correct, but a worn pin can have taper, scoring or a local step where the old ring moved. Installing a new bearing onto that pin can concentrate load and create fretting. During overhaul, measure the pin at several positions and directions rather than checking only one diameter.
Before pressing the bearing
- Confirm actual bore and pin measurements against the approved drawing.
- Check chamfers and corner radii so the ring seats fully against its shoulder.
- Remove burrs without damaging the bearing seat.
- Confirm the press tool contacts only the ring being fitted.
- Make sure thermal assembly methods, if used, are compatible with seals and liners.
After installation
A dimensional fit can pass inspection while the assembled joint still binds. Move the inner ring through the required angle, verify retainers do not clamp the ring incorrectly, and check that the pin turns or articulates as intended. If the joint becomes stiff only after bolting the structure together, look for bracket misalignment or housing distortion rather than forcing the bearing to move.
Need the full tolerance table?
Open the technical fitting-tolerance resource for H5-H8 and g5-h7 reference classes in metric and inch units.
