Specification summary of ISO 281 (dynamic load ratings and rating life) as it applies to 6400 series deep groove ball bearings: what the document fixes, where its scope ends, the ISO, DIN and GB/T equivalents, and the dimensions supplied to it.
ISO 281 — Scope
ISO 281 defines the basic dynamic load rating Cr (or Ca for a thrust bearing) and the method for calculating rating life from it. The rating is the constant load a bearing can carry for one million revolutions with 90% reliability; life follows L10 = (C/P)^p, with p = 3 for ball bearings and 10/3 for roller bearings, and the standard also gives the modified rating life that accounts for lubrication cleanliness and fatigue limit.
What ISO 281 Does Not Fix
It does not fix a bearing's dimensions, and it does not publish the rating for any particular bearing — the rating is declared by the manufacturer, computed to this method from the internal geometry, so two makers' figures for the same 6204 differ by a few percent and are not interchangeable in a life calculation.
This division of labour is the thing to carry away from any bearing standard. A boundary dimension standard makes bearings interchangeable; it does not make them equivalent. Two bearings of the same designation from different makers mount in the same seat and are not required to have the same load rating, the same internal design, the same cage or the same speed limit.
Dimensions Supplied to ISO 281
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) | Chamfer r min (mm) | Basic dynamic load rating Cr (kN) | Basic static load rating C0r (kN) | Limiting speed grease (rpm) | Mass (kg) |
|---|---|---|---|---|---|---|---|---|
| 6403 | 17 | 62 | 17 | 1.1 | 22.9 | 10.8 | 9000 | 0.325 |
| 6404 | 20 | 72 | 19 | 1.1 | 30.7 | 15.0 | 8000 | 0.465 |
| 6405 | 25 | 80 | 21 | 1.5 | 35.8 | 19.3 | 7000 | 0.630 |
| 6406 | 30 | 90 | 23 | 1.5 | 43.6 | 23.6 | 6300 | 0.850 |
| 6407 | 35 | 100 | 25 | 1.5 | 55.3 | 31.0 | 5600 | 1.15 |
| 6408 | 40 | 110 | 27 | 2 | 63.7 | 36.5 | 5000 | 1.50 |
| 6409 | 45 | 120 | 29 | 2 | 76.1 | 45.0 | 4500 | 1.90 |
| 6410 | 50 | 130 | 31 | 2.1 | 85.2 | 52.0 | 4300 | 2.35 |
| 6411 | 55 | 140 | 33 | 2.1 | 99.5 | 62.0 | 3800 | 2.85 |
| 6412 | 60 | 150 | 35 | 2.1 | 108 | 69.5 | 3600 | 3.45 |
| 6413 | 65 | 160 | 37 | 2.1 | 119 | 78.0 | 3400 | 4.15 |
| 6414 | 70 | 180 | 42 | 3 | 143 | 104 | 3000 | 5.70 |
| 6415 | 75 | 190 | 45 | 3 | 153 | 114 | 2800 | 6.65 |
National Equivalents
GB/T 6391 is the Chinese adoption; the static rating C0 is a separate document, ISO 76.
This product is supplied against ISO 15 / DIN 625-1 / GB/T 276, which names the documents it is made to.
When to Cite ISO 281
ISO 281 is the international reference and the right one to cite on a new drawing or a purchase specification. Adding the national equivalents alongside it costs nothing and makes the requirement legible to a supplier working to DIN or to GB/T.
