Before mounting the bearing to the shaft or housing, fix the inner ring or the outer ring, and move the other unfixed ring in the radial or axial direction, the amount of movement is called the bearing clearance, or the axial clearance.

The amount of clearance while the bearing is rotating (the so-called working clearance)shall have effects on the rolling fatigue life, temperature rise,noise,vibration and other functions.

In order to get the stable value of the clearance, normally a required load is put on the bearing in order to measure the bearing clearance.

Therefore, the measured value is larger than the true clearance (called the theoretical clearance), which means the amount of the elastic deformation caused by the load is increased. But for roller bearings, this elastic deformation can be ignored since it is comparatively small. Before the mounting of the bearing, the internal clearance is expressed with the theoretical clearance. ?

The selection of clearance

 If the amount of expansion or contraction of the rings caused by the interference fit when mounting the bearing on the shaft or in the housing is deducted from the theoretical clearance, then we have the "Mounting Clearance".

Furthermore, if the dimensional changes caused by the temperature difference inside the bearing are added to or reduced from the mounting clearance, we have the so-called "Effective Clearance".

When the bearing rotates while carrying a certain magnitude of load in the machine, if the elastic deformation caused by the load is added to the effective clearance, we then have the "Working Clearance".

When the working clearance is a slightly negative, the bearing has the longest service life. But with the negative clearance changing to be positive, the fatigue file shall decrease. Therefore, when choosing the clearance, it is preferred to choose the 0 or slightly positive working clearance.