51204 bearing
20 × 40 mm · dynamic rating 21.2 kN · static rating 37.5 kN. Dimensions, load ratings, designation meaning, life estimates and equivalent parts.
51204 specification
| Designation | 51204 |
| Type | Single-direction thrust ball bearing |
| Series | 512 light-medium |
| Bore diameter d | 20 mm |
| Outside diameter D | 40 mm |
| Basic dynamic load rating C | 21.2 kN (21,200 N) |
| Basic static load rating C0 | 37.5 kN (37,500 N) |
| Ratio C0/C | 1.77 |
| Speed guide, grease lubrication | 8,000 rpm |
| Life exponent p | 3 (ball bearing) |
Values come from the Rotec AI bearing catalogue and are indicative. Confirm against the manufacturer's current catalogue before ordering. Not every dimension (such as width) is listed here.
What the designation 51204 means
| Code | Meaning |
|---|---|
| 512 | Single-direction thrust ball bearing, light-medium series (flat seat washers) |
| 04 | bore code "04" = 4 × 5 = 20 mm |
Basic rating life of the 51204
Basic rating life is L10 = (C / P)p million revolutions, where P is the equivalent dynamic load and p = 3 (ball bearing). For a 51204 with C = 21.2 kN, the table shows what that gives at different load levels. It is the ISO 281 basic life only: it does not include lubrication, contamination, misalignment or reliability modifiers.
| C / P | P as share of C | L10 (million rev) | L10 at 1,500 rpm | L10 at 3,000 rpm |
|---|---|---|---|---|
| 3 | 33.3% | 27 | 300 | 150 |
| 5 | 20.0% | 125 | 1,400 | 690 |
| 8 | 12.5% | 512 | 5,700 | 2,800 |
| 12 | 8.3% | 1,728 | 19,200 | 9,600 |
For example, a C / P of 5 means the equivalent load is 4.24 kN on this bearing. Use the Load Calculator to work out P for your actual radial and axial loads.
Equivalents of the 51204
Brand-by-brand equivalents for this exact designation are not shown here. The Cross-Reference tool accepts SKF, FAG, NSK, NTN, Timken, Koyo and NRB designations, and shows what is catalogued.
Where the 51204 is used
Thrust ball / thrust roller bearings are chosen for: Predominantly axial load. Typical equipment: Vertical pumps, extruders, turbines, marine and heavy gear drives. Thrust roller for higher axial capacity and shock.
Other sizes in the same series
The 51204 belongs to the “512 light-medium” series. The next size down, the 51203, has a bore of 17 mm and a dynamic rating of 16.3 kN. The next size up, the 51205, has a bore of 25 mm and a rating of 26.5 kN (+25%).
Common problems on bearings like the 51204
Most field failures trace back to lubrication, contamination, fits and alignment rather than the bearing itself. These guides explain how to recognise and prevent them:
Questions about the 51204
What are the dimensions of a 51204 bearing?
The 51204 has a bore of 20 mm and an outside diameter of 40 mm. It is a single-direction thrust ball bearing. Series: 512 light-medium.
What is the load rating of a 51204 bearing?
In the Rotec AI catalogue the 51204 has a basic dynamic load rating C of 21.2 kN and a basic static load rating C0 of 37.5 kN. Always confirm against the manufacturer's current catalogue.
What is the equivalent of a 51204 bearing?
Use the Cross-Reference tool in Rotec AI to check brand equivalents for the 51204.