Ball bearing deflection

This determines how far the actual measurement is allowed from the nominal size. The nominal size is the size shown in the china high quality ball bearing Archives catalogue, for example the 6200 has a nominal bore diameter of 10mm, the 688 has a nominal bore diameter of 8mm etc. It is important to limit the maximum deviation from these dimensions. If there is no international tolerance standard (ISO and AFBMA) for bearings, this will depend on each manufacturer. This could mean that you order a 688 bearing (8mm bore) only to find out that it is a 7mm bore and won’t fit the shaft. Deviation tolerances generally allow a hole or outside diameter to be smaller than nominal size but not larger than nominal size.

Average pore diameter/outer diameter deviation

Or single-plane mean pore diameter deviation. This is an important tolerance when looking for a tight fit of an inner ring and shaft or an outer ring and housing. First, you need to understand that bearings are not round. Of course it’s not far off, but when you start measuring in microns (thousandths of a millimeter), you’ll see that measurements vary.

Bearing Width Deviation

Or the deviation of a single inner or outer ring width from the nominal dimension. It doesn’t need much explanation here. Like bore and outside diameter dimensions, width must be controlled within certain tolerances. Since width is usually less critical, the tolerance is wider than the bearing bore or outside diameter. A width deviation of +0/- 120 means that if you measure the inner or outer ring width at any point around a 688 (4mm wide) bearing, it should not be wider than 4mm (nominal size) or narrower than 3.880 mm.