Abstract: A gage for measuring a diameter of a workpiece has a pair of parallel spaced apart side rails. A pair of block sets is mounted between the side rails and spaced apart from each other. A pair of arms extends transverse to the rails through mating profiles in the blocks of each block set. The arms are slidable in a transverse direction to the side rails. Each block set can slide along the side rails and has a single fastener that secures the blocks to the side rails and the arms to the blocks in a desired position. Drag brakes between the blocks and the side rails prevent the components from sliding of their own weight while the fasteners are loosened. The block sets and arms are rotatable 180 degrees about the fasteners when loosened to accommodate outside and inside measurements.