The RL0402E012M300K is an electronic component manufactured by Ruilongyuan and is a type of varistor. It is a 0402 (1005 metric) size, meaning it is 0.04 inches (1 millimeter) in length and 0.02 inches (0.5 mm) in width. It has a rated voltage of 12 Volts (V), an operation voltage of 50 V, and a capacity of 300 kiloohms (KO). It is RoHS compliant, meaning it meets the European Union's directive on hazardous substances.