Abstract: The present invention relates to a testing device for magnetically testing while uninterruptedly moving along an elongated magnetically permeable object having intermittent supports to one side thereof. The device which is arranged to close around the test the object from all sides other than at the supports and to open at and clear past the supports while continuing to move, comprises first and second housing sections hingedly connected to one another with the first housing section being adapted to maintain the device in a testing position relative to the object and the second housing section being moveable relative to the first housing section for opening and closing the device around the object. An actuator is provided for effecting such opening and closing with a control for operation of the actuator without manual assistance at the device.