Heretofore, it has been known to provide various protective guards or shields to reduce injury to operators of various types of machines in the metal forming industry. In many applications, it is a requirement that various of the machine tools be provided with such protective devices to reduce accidental injury to the machine operators. In such instances, it has been known provide what is commonly referred to as a "light curtain" which system generally includes an energy source (i.e. electrode and/or light beam, laser and the like) and a receiver for the energy source that provide, in effect, a barrier or curtain. If this barrier or curtain is broken, such as by the operator's extremity (i.e. arm or hand) blocking transmission of the energy source to the receiver the electrical system is energized, as known in the art, to automatically turn-off operation of the machine tool thereby preventing injury to the operator. For example, by preventing closing of the metal forming die in a punch press prior to the time when the operator's extremity may have otherwise been accidentally inserted between the dies during closing thereof. However, in such prior light curtain systems, the components thereof, have generally been disposed in a fixed or stationary mode thereby limiting the general flexibility and usability of the system on various type machines and/or for working on various sizes and/or shapes of metal parts to be formed. Accordingly, while prior light curtain systems have been satisfactory from a safety standpoint, they have not been entirely satisfactory in providing a mounting assembly therefore which enables the component parts of the system to be selectively adjusted and articulated to accommodate various sizes and shapes of a metal workpiece and to enable the set-up operator to quickly and easily effectuate the proper die setting.