P6X is a class defined for tapered roller bearings: the dimensional tolerances of P6, with tighter running accuracy on the cup and cone. It exists because a tapered roller bearing carries the shaft position on its cone back face, so runout of that face translates directly into gear or wheel runout.
In a tapered roller bearing the axial position of the shaft is set by the cone back face, not by the raceway. Any wobble in that face becomes axial float once per revolution, which in a gearbox becomes mesh error and noise. P6X tightens that face specifically, which P6 alone does not do.
It does not correct a badly machined housing shoulder, a shaft with poor squareness, or an incorrect axial setting. Tapered roller bearings are set by end play or preload at assembly; if that setting is wrong, no tolerance class will compensate.
| Applies to | Tapered roller bearings |
|---|---|
| Equivalent to | P6 dimensions with tighter runout |
| Typical runout | Around 4 µm for a 30 mm bore |
| Price relative to P0 | 150–190% |
| Typical use | Gearbox pinions, differentials, wheel ends |
| Why it exists | Cone back-face runout maps onto gear mesh error |
| Not applicable to | Deep groove ball, cylindrical roller |
| Criterion | P6 | P6X | P5 |
|---|---|---|---|
| Dimensions | Tighter than P0 | As P6 | Tighter than P6X |
| Radial runout | ~6 µm | ~4 µm | ~4 µm |
| Cone back-face runout | Standard | Tightened | Tightened |
| Price | 130–160% | 150–190% | 200–300% |
| Availability | Common | Common in gearbox sizes | Limited |
| Typical use | Gearbox | Pinion, differential | Precision gearbox |
This category covers everything outside the standard catalogue: thin-section and miniature bearings,…
Read →A tapered roller bearing uses conical rollers running between conical raceways whose apexes meet on the…
Read →A cylindrical roller bearing uses cylindrical rollers in line contact with the raceways, which gives a high…
Read →No. P6X is defined for tapered roller bearings; for ball bearings the equivalent step is P6 or P5.
Because the application needs the tighter cone back-face runout that P6X specifies and P6 does not. It is a deliberate specification, not a supplier variation.
Physically yes, functionally risky: runout of the cone back face is what drives gear mesh error, and that is exactly what P6 does not tighten.
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