This particular part is a Polytronics PMV0603-8R0G SMD varistor with an 18V rating, 5.5V rating and 4V rating, and is compliant with Restriction of Hazardous Substances (ROHS) environmental regulations. Varistors are non-linear passive electrical components which have a voltage-dependent resistance in order to protect against power spikes in circuits. SMD varistors are used for control and power-supply line protection, and have a small footprint to accommodate a wide range of circuit designs. The PMV0603-8R0G is ideal for applications such as overvoltage and lightning protection, ESD protection, communication protection and automotive power modules.