The Aircraft Connector Tester is a Go/No-Go device that is utilized to determine whether the aircraft 400 Hz pins are worn beyond accepted tolerances. Simply try to insert the gauge over the appropriate pin. If the gauge slides over the pin, the pin is worn and the aircraft connector must be replaced as this indicates a worn or loose contact.

“A worn or loose contact on one or more of the pins in the connectors can cause high contact resistance which results in a hot plug; in some cases a fire or loss of a phase or control voltage (E&F) which causes the aircraft to reject the external 400 Hz power.”

Excerpt from SAE information report, "400 Hz Connection Aircraft Electrical Maintenance Procedures," issue 1994-12.