Abstract: A gauge for measuring the depth of a hole countersink in a workpiece for a fastener, or for measuring the protrusion height of a fastener head above the surface of the workpiece, includes a tapered cylindrical case for holding a transducer such as an LVDT, and a probe assembly removably mounted on the lower end of the case. The probe assembly includes a foot having an annular contact ring at its lower end for contacting the workpiece around the hole or around the fastener head to establish the reference position from which the measurement is to be taken. A probe is mounted in a well in the foot for axial sliding movement therein and is captured within the food by a connector which is screwed onto the upper end of the foot.