Miniature & Instrument Bearings

Shield & Seal Types

Shields and seals are protective closures which retain lubricants and assist in preventing contaminants from reaching internal surfaces. In torque-sensitive applications, it may be advantageous to use shields rather than seals because there are no contacting surfaces to create drag.

The following chart illustrates the more common type of shields and seals.

Consideration should be given to the compatibility of cage and shield type designs to allow for appropriate clearance. Consult with NPB for availability.

Description Type Design Material Operating
Temp. Max.
Shield - Removable with snap wire. Minimal clearance. Most Popular Z Stainless Steel
300 Series
Seal-Removable with snap wire. Minimal clearance to light contact. Low torque. L Glass-reinforced PTFE 400F
Seal - Excellent sealing characteristics. D Buna-N Bonded to Steel Insert 250F
Seal - Excellent sealing characteristics.
High cost.
D1 Viton® Bonded to Steel Insert 400F

Characteristic ABEC 1 ABEC 3P ABEC 5P ABEC 7P ABEC 9P
Bore Tolerance Limits +.0000 +.0000 +.0000 +.0000 +.0000
–.0003 –.0002 –.0002 –.0002 –.0001
Bore 2 pt. out of Roundness .0001 .0001 .00005
Bore Taper .0001 .0001 .00005
Radial Runout .0004 .0002† .00015 .0001 .00005
Width Variation .0002 .0001 .00005
Bore Runout with Face .0003 .0001 .00005
Race Runout with Face .0003 .0001 .00005

* Measument in inches.
† Add .001 to the tolerance if bore is over 10mm (.3937 inch)

Miniature and Instrument Ball Bearings Inner Ring *
The ABEC tolerances listed are current at this catalog’s printing. These tolerances are reviewed regularly and updated as required. The ABMA standards may be obtained by contacting:, 1101 Connecticut Ave. N.W., Suite 700, Washington, DC 20036.