Abstract: The gage includes a cam follower formed of a plurality of radially expande segments each provided with a pair of inclined surfaces riding on a pair of cams carried by an elongate shaft reciprocably mounted in a suitable housing. When reciprocated in one direction one of the cams radially expands the segments. Upon reverse reciprocation, the other cam contracts them. Threads formed on the segments are formed ot mesh with the threads to be measured. A primary function of the gage is to measure the concentric relationship between a cylindrical object and the cylindrical configuration of a threaded end portion of the object. For this purpose, the shaft is floatably supported and, as the threaded segments move into their meshed engagement, it floatably assumes the axis of the threads being measured. When fully meshed, non-contact transducers can measure any inclination of the shaft from an original disposition.