Felt Sealed Ball Bearing Nomenclature and Numbering System

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3D CAD image of a Felt Sealed Ball Bearing from AST BearingsThe felt sealed ball bearing falls within the product category of deep groove ball bearings.  The characteristics of this group are wider inner or outer rings and the original production designs used a metal shield with a felt ring on one or both sides of the bearing.  However, most of the designs in production today have switched to a heavy duty rubber seal to replace the felt.

Numbering System for the Felt Sealed Ball Bearings:

  • 88000 Series:  The inner ring is wider than the outer ring, two felt seals.
  • 87000 Series:  The inner ring is wider than the outer ring on one side and slightly recessed on the other; one felt seal on the extended side, shielded on the other side.
  • WC88000 Series:  The inner ring is wider than the outer ring on one side, two felt seals.
  • WC87500 Series:  The inner ring is flush with the outer ring on one side and slightly recessed on the other; one felt seal and one metal shield.

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Bushing Tolerances

Wrapped Bushings


It is not possible to accurately measure the external and internal diameters of a wrapped bushing in its free condition. In the free state, a wrapped bushing will not be perfectly cylindrical. The bushing will conform to the housing when the split is tightly closed. For this reason the OD & ID of a wrapped bushing can only be checked with special gauges and test equipment.


Below is an example on how to determine the bushing’s ID & OD tolerances with respect to the mating shaft and housing tolerances after installation:


Units: mm


The chart and diagram shows that after installation this bushing will have a total OD tolerance of 0.030 mm. Also, the ID tolerance is 0.065 mm after installation.


Standard Bushings (non-wrapped)


Standard bushing tolerances are specified on their respective dimension tables. For example:



Units: mm


If a bushing with an 8 mm ID (d) and a 12 mm OD (D) is used, the ID (d) dimension specifies an F7 tolerance which corresponds to 13 µm / 28 µm. The OD (D) dimension specifies an m6 tolerance which corresponds to 7 µm / 18 µm.


Note:  Uppercase tolerances refer to different values from lowercase tolerances.

AST Bearings is proudly presenting our new certificates for both the NJ and CA locations: AST Bearings’ ISO 9001:2015 Certificates

To learn more about what the ISO 9001 standard is, the differences between the 2015 and 2008 versions, and how AST verifies customer satisfaction: Learn About AST Bearings’ certification to ISO 9001:2015

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