Keysight NFA Series Performance Verification And Calibration Manual page 191

Caring for Connectors
Using Connector Gages
Measuring Connectors
Measuring the recession of the center conductor behind the outer
conductor mating plane in a connector is done in exactly the same way as
zeroing the gage, except of course that the graduated dial is not re-set
when the measurement is made.
If the connector has a retractable sleeve or sliding connector nut -
precision 7mm connectors, for example - extend the sleeve or nut fully.
This makes it easier to keep the gage centered in the connector.
Hold the gage by the plunger barrel and slip the gage into the connector
so that the gage plunger rests against the center conductor. Carefully
bring the gage into firm contact with the outer conductor mating plane.
Apply only enough pressure to the gage so that the gage pointer settles
at a reading.
Gently rock the connector gage within the connector, to make sure that
the gage and the outer conductor have come together flatly. Read the
recession (or protrusion) from the gage dial. (For maximum accuracy,
measure the connector several times and take an average of the
readings.)
Rotate the gage relative to the connector between each measurement. To
monitor connector wear, record the readings for each connector over time.
Appendix E 171