P5 is the class most machine tool builders specify for the front position of a spindle that does not need P4. Runout drops to about 4 µm on a 30 mm bore, bore and outer diameter tolerances tighten to match, and the price roughly doubles against P0. It is also the point at which the bearing stops compensating for the housing and starts demanding it.
Beyond runout, P5 tightens the parallelism of the raceways and the variation of the width, and it constrains the position of the contact angle in angular contact bearings. That matters because in a spindle the bearing pair is preloaded; any mismatch between the two bearings turns into a tilt that the preload amplifies.
A spindle housing bored to IT7 with a shoulder out of square by 10 µm will tilt a P5 bearing and produce more error than the bearing's own runout. If the measured runout after assembly is worse than the class promises, check the shoulder squareness and the fit before returning the bearing.
P5 bearings are usually run at higher speed and with less clearance, so grease selection and fill quantity become critical. Overfilling a P5 spindle bearing is a common cause of overheating — the grease has nowhere to go and churns.
| Also written | Class 5, ABEC-5, DIN P5 |
|---|---|
| Typical radial runout | Around 4 µm for a 30 mm bore |
| Price relative to P0 | 180–260% |
| Housing requirement | IT5-IT6 bore, square shoulder |
| Preload | Usually specified — paired or spring preloaded |
| Typical use | Machine tool spindles, high-speed motors, precision gearboxes |
| Availability | Common in angular contact and deep groove |
| Not required for | Conveyors, pumps, fans |
| Criterion | P6 | P5 | P4 |
|---|---|---|---|
| Radial runout (30 mm) | ~6 µm | ~4 µm | ~2 µm |
| Raceway parallelism | Standard | Tightened | Tight |
| Housing requirement | IT7 | IT5-IT6 | IT5 |
| Price | 130–160% | 180–260% | 300–450% |
| Typical speed | Up to 10,000 rpm | Up to 20,000 rpm | 20,000 rpm and above |
| Preload | Optional | Normally specified | Always specified |
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Read →For most general milling and turning spindles, yes. Grinding and high-speed machining usually need P4 because the error budget is measured in single micrometres.
You can, but you will not get P5 accuracy. The bore tolerance and shoulder squareness of the housing set a floor on the assembly runout.
For angular contact spindle bearings, yes — they are normally supplied as a matched set with defined preload. For single deep groove bearings no pairing is required.
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