14D821K is a Varistor, also known as a voltage-dependent resistor (VDR), manufactured by Ruilongyuan with a voltage rating of 670V and 4.5KA peak current rating. It is designed with a through-hole mounting style for easy assembly on printed circuit boards (PCBs), and is RoHS compliant, meaning it meets the European Union's environmental requirements for the elimination of certain hazardous substances in electronic products. It helps to protect electronics from spikes in voltage or transients, and is frequently used in power supplies, switch mode power supplies, electrical appliances, and telecommunications equipment.