A measuring head clamp-on device for ultrasonic flow measuring heads includes a guide element for receiving at least one measuring head protective housing for at least one measuring head and includes at least one clamping unit connected to the guide element, and thereto connected clamping device for detachably fastening the guide element to the measuring tube, wherein the guide element is non-positively or positively connected to at least one apparatus for centering and clamping the same on the measuring tube, so that the guide element is oriented and fastened parallel and with a defined distance to the apex of the measuring tube irrespective of the tube diameter.