Abstract: A pair of anvil pins are mounted at their lower ends on a pair of spaced carriers, which reciprocate beneath a work supporting surface in horizontally spaced, colinear paths. The pins project upwardly through an elongate slot in the work surface and into a bore in an annular workpiece positioned on the surface. One carrier is urged by a spring in one direction to cause its anvil pin to urge the outer periphery of the workpiece into a V-shaped recess in a locator plate that is adjustably secured on the work surface, thereby to center the workpiece over the slot. An indicator mounted on the other carrier has a resilient probe extending between the carriers to urge them apart, and thereby to urge their pins against diametrally opposite sides of the bore, whereby a readout on the gage will indicate the extent to which the I.D. of the bore differs from a predetermined value. One pin is adjustable on its carrier to accomodate the gage for measuring particularly large or small bores.