12.43mm Dia, 2" Long Vermont Gage Class ZZ Plus Pin Gage, manufacturer part number 912312430.
Specifications: Diameter of Measurement: 12.43 mm; Gage Function: Go (Plus); Class: ZZ; Tolerance: 0.005 mm; Surface Finish: 10 Micro Finish; Overall Length: 2.0000 in.
Material: Tool Steel. Coating/Finish: Black Oxide. Unit of measure: Metric.