Abstract: A magnetic sensing device for determining the presence of a non-magnetic portion of an otherwise magnetic metal workpiece, including a body which is adapted to be brought into close proximity to a surface of the workpiece and to be moved along that surface and which carries a magnet movable relative to the body between an active position near the workpiece surface and a retracted position farther away from that surface, with the magnet being retained in its active position near the surface when received opposite a portion of the workpiece which is formed of magnetic metal and being spring urged away from the surface of the workpiece and from the active position of the magnet to its retracted position when the magnet is received opposite a non-magnetic portion of the workpiece, and a manual actuator which is movably carried by the body and has a portion exposed for manual actuation when the body is in its position of use closely proximate the workpiece surface, and which is adapted upon manual actuation to dis