Abstract: The device comprises a body having a longitudinal central bore for passing a probe therethrough intended to penetrate into the hole to be tested. The probe is fixed to the body by a matching socket having a locking screw. A ring is slidably mounted on the body, and secured against rotation by a screw engaged in a longitudinal groove of the body. A spring pushes the ring back with respect to the body, the movement being limited by a stop. The front part of the ring receives an insert stop coming to bear against the outer face of the workpiece to be tested. At the end of penetration of the probe into the hole, the rear part of the ring comes opposite an annular mark formed in the body.