Ring Gage Calibration


The purpose of this procedure is to provide general instructions for the calibration of ring gages.


This general procedure shall be used in the absence of any specific calibration procedure for ring gages.


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 ring gage(s) 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. Using an arkansas stone to remove nicks and burrs.
  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 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.

The following are "nominal diameters" and tolerances for ring sizes up to 8 inches.


Nominal Diameter Tolerance
Up to 0.500 Inches 25 Microinches
0.5001 to 4.000 Inches 50 Microinches
4.0001 to 8.000 Inches 100 Microinches
Up to 0.500 Inches 25 Microinches
0.5001 and Larger 100 Microinches

Equipment Required

The Standards listed below should be selected on the basis of their higher accuracy level when compared to the IUT. 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 Uncertainty
Gage Blocks * +/- 1.7 µ inch
Gage Blocks * +/- 8 µ inch 2
Internal Measuring Machine +/- 1 µ inch **
Internal Measuring Machine +/- 5 µ inch **
Precision Parallels Part of Gage Block Set

* Use corrections when required.

** When the standard gage blocks listed are used as described in the detailed procedure, the internal measuring machine will repeat the measurement within the stated uncertainty.

Note: The wringing quality of the gage blocks must be sufficient to hold the parallels and gage blocks together without depending on the clamping rod. Errors may occur if wringing is ignored.

Detailed Procedure

  1. Wring the gage blocks and the precision parallels together for the nominal diameter to be measured.
  2. Place the gage blocks and the IUT on the internal measuring machine to temperature stabilize.
  3. Set the precision parallels/gage blocks on a pair of friction rolls over the outside of the stylus and zero the internal measuring machine to the gage blocks.
  4. Replace the gage block with the IUT. Turn the IUT until the size markings are normal to the stylus of the measuring machine.
  5. Measure the diameter of the IUT at the bottom, middle, and top.
  6. Turn the IUT 90 degrees and repeat step 5.

Reason for Reissue

Revision A - First Release