Starting friction torque for instruments – ball bearings
The maximum value for the starting friction torque stated in the table is taken from the AFMBA standard for instrument ball bearings. They apply to ball bearings in ABEC 7P quality (with or without shields), both in stainless steel (e.g. AISI 440C) and in chrome steel (AISI 52100), with a two-piece cage and lubricated with instrument oil.
The definitions and test conditions are specified in this standard. These values are maximum values for myonic ball bearings of the relevant category.
| Bore diameter | Outer diameter | Test load | Maximum starting frictional torque μN . m | ||
| d | D | Internal radial clearance | |||
| zoll | zoll | N | Press fit | Normal fit | Loose fit |
| .0001“- .0003“ | .0002“- .0005“ | .0005“- .0008“ | |||
| 2-8 μm | 5-12 μm | 12-20 μm | |||
| .0400 | .1250 | .75 | 18 | 15 | 14 |
| .0469 | .1563 | .75 | 18 | 15 | 14 |
| .0550 | .1875 | .75 | 18 | 15 | 14 |
| .0781 | .2500 | .75 | 18 | 15 | 14 |
| .0938 | .3125 | .75 | 18 | 15 | 14 |
| .1250 | .2500 | .75 | 18 | 15 | 14 |
| .1250 | .3125 | .75 | 18 | 15 | 14 |
| .1250 | .3750 | .75 | 20 | 15 | 15 |
| .1250 | .3750 | 4 | 50 | 45 | 42 |
| .1250 | .5000 | 4 | 50 | 45 | 42 |
| .1563 | .3125 | .75 | 18 | 15 | 14 |
| .1875 | .3125 | .75 | 18 | 15 | 14 |
| .1875 | .3750 | .75 | 20 | 16 | 15 |
| .1875 | .5000 | 4 | 65 | 55 | 50 |
| .2500 | .3750 | .75 | 18 | 15 | 14 |
| .2500 | .5000 | 4 | 60 | 52 | 48 |
| .2500 | .6250 | 4 | 70 | 60 | 55 |
| .2500 | .7500 | 4 | 80 | 70 | 65 |
| .3750 | .8750 | 4 | 110 | 95 | 90 |