Abstract: An apparatus for automatically engaging and measuring a spline of a workpiece with a gauge having first and second relatively rotatable sensing elements. The elements are rotatable to a first axially aligned position for insertion into grooves between adjacent teeth of the spline and to a second angularly displaced position to bear on opposed faces of adjacent teeth to clamp the spline in the gauge and measure the spline. The gauge elements are inserted in the grooves by moving the gauge and workpiece together with a lost motion to bear on each other adjacent an end of the spline and then rotating the gauge to align the elements with and start them into the grooves. Thereafter the elements are axially advanced fully into the grooves and then rotated to their second position.