Hole Micrometer Calibration


The purpose of this procedure is to provide general instructions for the calibration of hole micrometers.


This general procedure shall be used in the absence of any specific calibration procedure for hole micrometers.


The Hole Micrometer is a series of precision tools designed to accurately measure the inside diameter of holes from 0.080 to 0.280 inches. The probe end of the tool is designed to assure accuracy of measurement over the entire range. The probe movement fixes one side of the probe and allows the other half of the probe to move parallel to the stationary side. With this design and the leaf-spring mechanism, these tools provide an accurate measurement of small hole diameter.

Preliminary Instructions and Notes

  1. Read this entire procedure before beginning the calibration.
  2. Calibration shall be performed in an environment that conforms to Manufacturer Specifications.
  3. The hole micrometer will hereafter be referred to as the Instrument Under Test (IUT).
  4. Verify that the IUT is clean.
  5. Visually examine the IUT for any condition that could cause errors in the calibration.
  6. Check the mechanism for smooth operation.
  7. Check the TI with two points within its range.
  8. If any of the requirements cannot be met, refer to the applicable manufacturer manual.
  9. If a malfunction occurs or a defect is observed while calibration is in progress, the calibration shall be discontinued and necessary corrective action taken; if corrective action affects a measurement function previously calibrated, the function shall be recalibrated before the remainder of the procedure implemented.

Reference Material

Applicable Manufacturers Manual or Brochures.


The specifications of the IUT are determined by the applicable manufacturer's documentation. If the manufacturer's documentation is not available, then the specifications identified in this procedure are used.

Equipment Required

The Standards listed below should be selected on the basis of their higher accuracy level when compared to the unit under test. Equivalent Standards must be equal to or better than the Minimum-Use-Specification.

Minimum-Use-Specifications for Standards listed are 1/4 the accuracy required by the IUT.

Required Equipment

Standards Used Range Tolerance
Standard Ring Gages 0.080 to 0.300 inch +/- 0.00005

Detailed Procedure

  1. Select two standard ring gages within the range of the IUT.
  2. Insert the probe end of the IUT into the ring gage.
  3. Rotate the micrometer on the end of the IUT until contact is made with the standard ring. Continue to rotate the micrometer spindle until the ratchet clicks a minimum of three times.
  4. Compare reading of IUT with size of standard ring gage.
  5. Repeat steps 2 through 4 for the second ring gage.

Reason for Reissue

Revision A - First Release