What is the primary function of the IDG-1 internal diameter gauge?
The IDG-1 checks that the small end of a gauge fits within the internal diameter of a cap, used as a pass/fail reference check on closures.

How does the IDG-1 perform its pass/fail check?
The IDG-1 works as a go/no-go gauge for crown cap internal diameter: the smaller end must fit inside the cap opening (go condition) while the larger end must not (no-go condition). Any deviation from these reference dimensions immediately indicates a dimensional non-conformity.

With which other AT2E instruments is the IDG-1 typically used?
The IDG-1 is used alongside the ODG-1 outer diameter gauge and the HDC Crown Cap Height and Thickness Gauge to perform a complete crown cap dimensional control check, covering internal diameter, external diameter, height, and thickness in a single inspection sequence.