In the NSK bearing size chart, NSK uses four definitions of speed shown in table below.
| Speeds | Overview | Applicable lubrication methods |
|---|---|---|
| Limiting Speed (Grease) | Empirically obtained and comprehensive bearing limiting speed in grease lubrication. | Grease lubrication |
| Limiting Speed (Oil) | Empirically obtained and comprehensive bearing limiting speed in oil bathlubrication. | Oil bath lubrication |
| Thermal reference Speed | Rotational speed at which equilibrium is reached between the heat generated by the NSK bearing and the heat flow emitted through the shaft and housing under the reference conditions defined by ISO 15312. One among warious criteria showing the suitability for operation at high speed. | Oil bath lubrication when subject to reference conditions outlined in ISO 15312 |
| Limiting Speed (Mechanical) | Mechanical and kinematic limiting speed achievable under ideal conditions for lubrication, heat dissipation and temperature. | e.g. Properly designed and controlled forced-circulation oil lubrication |