An ultrasound device for the treatment of surfaces and welded joints is disclosed. The device has a housing with a plurality of shaped slots formed therein. A reciprocally moveable sleeve is attached to the housing, and contains an ultrasonic transducer. A reciprocally moveable attachment is attached to an operating end of the sleeve, and has a detachable working head mounted thereon. A pin is positioned in a pin slot on the housing, and anchors the sleeve to the housing to limit movement of the sleeve. The pin is biased towards the front of the pin slot by means of a spring, and a moveable spigot provides a predetermined contact force between the ultrasound device and a work surface. The spigot has spigot pins that are inserted into the plurality of shaped slots in the housing in order to restrict axial movement of the spigot, thereby providing added compression or tension to the spring in order to provide the predetermined contact force.