The crack gauge helps determine the width of a crack by comparing it to the printed lines on the card.

Left Side: 2in Scale
Right Side: 50mm Scale
Top: .004", .006", .008", .010", .012", .014", .016", .020", .025", .030", .040", .060", .080", .100"
Bottom: 2.5mm, 2mm, 1.5mm, 1mm, .80mm, .60mm, .50mm, .40mm, .35mm, .30mm, .25mm, .20mm, .15mm, .10mm