Tolerance class P4 is the bearing tolerance grade per ISO 492, one step above P5 and equivalent to ABEC 9 in the ABMA system, used for high-speed grinding machines, precision machine tool spindles, and aerospace equipment — where inner ring radial runout ≤ 2.5 µm is required.
At P4, most manufacturers shift to make-to-order production rather than mass production. 100% individual inspection of every bearing using laser measurement and air-gauge interfaces is mandatory. See how P4 compares to P5 and P6 at bearing precision classes and browse deep groove ball bearings in P4 precision for ultra-high-speed spindles. P4 bearings cost 5–15× more than equivalent P0, depending on manufacturer and size.
P4 is not the choice for equipment that is merely "high precision" in general terms. It is the grade for drive systems with extremely tight technical constraints: workpiece surface finish Ra ≤ 0.1 µm, spindle speeds of 25,000–60,000 rpm, or dynamic balancing requirements at grade G0.4.
P4 Parameters and Applications
ISO 492 specifies the following for P4 with ball bearings d = 18–30 mm:
- Δdmp (inner bore tolerance): 0 / −5 µm
- Kia (inner ring radial runout): ≤ 2.5 µm
- Kea (outer ring radial runout): ≤ 3 µm
- Sd (face runout): ≤ 4 µm
Typical application: angular contact ball bearing 7205 BECBP/P4 (d = 25, D = 52, B = 15 mm) mounted as back-to-back (DB) pair on a CNC surface grinding spindle running at 40,000 rpm. Total spindle runout when tested is ≤ 2 µm — required for a grinding wheel to achieve Ra 0.05 µm on hardened steel workpieces.
| Parameter | P5 | P4 | P2 |
|---|---|---|---|
| Kia — d = 18–30 mm | ≤ 4 µm | ≤ 2.5 µm | ≤ 1.5 µm |
| Kea — d = 18–30 mm | ≤ 5 µm | ≤ 3 µm | ≤ 1.5 µm |
| Suitable speed | 15,000–25,000 rpm | 25,000–60,000 rpm | > 60,000 rpm |
| Manufacturing inspection | 100% per unit | 100% + laser measurement | 100% + ISO cleanroom |
| Cost vs. P0 | 2–5× | 5–15× | 20–50× |