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Additional Tips on Plug Gage Use

Courtesy Van Keuren

Certain practical considerations are advisable to insure that plug gages are used correctly.

  • Holes to be gaged should be as clean as possible and free from burrs which would interfere with insertion.
  • The gage should of course be aligned with the hole for insertion; however, there are some gage features which can aid in this. A chamfer or radius on the gage end will help guide the gage into the hole. In addition, the GO gage may be vented for gaging blind holes so the air pressure within the hole will not interfere with the insertion of the gage.
  • The gage should be turned into the work slowly and carefully. A good fit will be snug. A plug gage should never be forced into a part.
  • In using a NOGO gage you should be certain that the gage is truly unable to enter the hole before the part is accepted. The procedure which is normally made to insert the GO gage should be followed to insure that the NOGO gage is being properly used.
  • When gaging steel the temperature of a steel gage and the part should be the same. Where the materials differ, however, such as tungsten carbide gage or a non-steel part, consideration should be given to actual temperature since the coefficients of expansion of the materials will differ. Standard temperature is 20 C (68 F). Gages are always calibrated at this temperature, and when the product is also at this temperature accurate gaging is insured.
  • Gages should be carefully protected against prolonged exposure to heat and moisture. After cleaning gages should be oiled carefully with a rust inhibitor and stored in containers or cases protected with rust inhibitor.
  • Any program of gage use should include periodic inspection of the gages to insure that they are not worn below tolerance or have otherwise become scratched or marred. GO gages are, of course, subject to more wear and should, therefore, be inspected more frequently. If a GO gage has worn below its tolerance it will begin to accept undersized holes. Excess wear on the NOGO gage, while not as common, will still interfere with the intended use of the gage. The more the NOGO gage wears the more acceptable parts may be rejected. Unlike the GO gage, unacceptable parts will never be accepted; however, the rejection of good parts may still be a costly price to pay for not having properly checked the NOGO gage.