Color-Coded Probe 3-6-9-12 mm markings with #23 Shepherd’s Hook Explorer. Expros combine an Explorer tip and a Probe tip into one easy-to-use double-end instrument. The millimeter measurements are precisely cut into the Probe tips. Colorcoding is applied to probes under extreme temperatures so that the color penetrates the surface of the tip. Probe tips undergo additional tighttolerance grinding to achieve the desired readability for each marking. Explorers are hand-sharpened to a point.