Checkline K-300 [K-300-E] Analog Metric Thickness Gauge, Range 0-30mm, Depth Of Jaw 300 mm, Feeler E For Sheet Metal, Etc. Measuring Range: 0 - 30 mm / 0 - 1.00 inch, Resolution: 0.005 inch / 0.1 mm, 11.80 inch (300 mm) Jaw Depth. The Checkline K-300 thickness gauge features an easy to read analog display along with the high accuracy. The K-300 model is available with 5 different feelers, which can be found below. Measurement is done by a spring force. Opening by lifting device (lever) - self closing.