Checkline FD-50 [FD-50-D] Digital Thickness Gauge, 0 - 12.5 mm / 0.4 inch Range, Depth Of Jaw 50 mm With 10mm Footers, Feeler D For Hard Leather, Plywood, Fiberboard. Measuring Range: 0 - 12.5 mm / 0 - 0.5 inch, Resolution: 0.001 mm / 0.0001 inch. The FD-50 digital thickness gauge series features an easy-to-read LCD display with the ability to display thickness in mm or inches. The FD-50 digital thickness gauge model is available with 5 different feelers, which can be found below. A self-closing mechanism provides accurate and repeatable measurements.