The Ultratec MS5918 is a 6 volt, 3 watt replacement bulb for older Ultratec lights. The supplier lists it as the spare bulb for the Ultratec MS5124, MS5132 and MS5912 models, so if one of those lights still works but the bulb has blown, this part gets it going again without buying a new unit. Compare the voltage, wattage and base of the bulb with the one you are replacing before fitting it. The part is discontinued, so it is a good idea to keep a spare for lights you use often, such as farm or emergency lamps.