Groove Micrometer Calibration


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


The groove micrometer gages is considered an in an inherently stable device and will not require recalibration unless a special request is made by the user.


The Groove Micrometer is a precision tool designed for measuring grooves, recesses and shoulders located inside bores to a high degree of accuracy. The tool is capable of measuring four different types of measurements: outside measurement, inside measurement, edge-to-edge measurement, and with the locating disk, end to edge measurement. The disc thickness must be added to the micrometer reading for certain applications. The locating disk is lapped to minimize parallax and to provide tool accuracy.

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 groove 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. If any of the requirements cannot be met, refer to the applicable manufacturer manual.
  7. 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 groove micrometers are determined by the applicable manufacturer's documentation. If the manufacturer's documentation is not available, then the following specifications are used.

Range & accuracy of gages covered by this procedure as follows: Range of Gage: Zero to 1.0", 1.0 to 2.0", 2.0 to 3.0" 3.0 to 4.0". Accuracy: (0.001" within the working range of the gage. Gaging disc is 0.025" (0.001").

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 Minimum-Use-Specifications
Gage Blocks Gage 3 Range: 0.010 to 4.000 inch
Tolerance: + 0.000006 inch
- 0.000004 inch
Outside Micrometer Accuracy: +/- 0.001 inch

Detailed Procedure

  1. Select gage blocks of a size equal to 25, 50, 75 and 100 percent of the IUT full range.
  2. Select the smallest gage block and position it between the gaging disk of the IUT. Rotate the micrometer thimble until contact is established with the gage block.
  3. Compare reading of the IUT with size of gage block.
  4. Repeat steps 2 and 3 for remaining three gage blocks referenced in step
  5. Using the outside micrometer verify the size of both gaging disc.

Reason for Reissue

Revision A - First Release