Nationwide Bearing Co Ltd

Bearing Tolerances

A bearings accuracy is split between three different aspects, the external dimensional accuracy, the running accuracy and the machining accuracy

Accuracy of External Bearing Dimensions
This measures the accuracy of the external dimensions of the bearing such as the bore, outer diameter, inner ring width and outer ring width. The difference between the actual measurement and the expected measurement is referred to as the dimensional deviation. The accuracy of the dimensions is important for determining shaft and housing fits.

Machining Accuracy
The machining accuracy measures the variation of the dimensions when measured on a single bearing and then compared to one another. The variation is then the difference between the largest and smallest measurement on the bearing while the mean variation is taken as the average dimensional difference of the measurements taken. This is important for determining the precision of the manufacturing process and is important when considering tolerances for shafts and housings

Running Accuracy

Running accuracy is generally referred to as the runout and is a measure of the degree of eccentricity (for radial runout) and “squareness� (for bore and outer diameter) of the bearing. The measurements most often used are that of the inner and outer ring radial runout, a bearing with a high degree of radial runout will produce a greater vibration than a bearing with a low degree of radial runout, this becomes more noticeable at higher speeds.

Below is a table of the international standards for bearing accuracy