The CMFX 503F3950 0402 NTC Thermistors ROHS is a pretty small, surface-mount component manufactured by Shiheng. It is used in a variety of applications from filtering and impedance matching to thermal sensing and power control. The type of thermistor used in this component is called a negative temperature coefficient (NTC) thermistor, which sees its resistance decrease as temperature increases. The 0402 size spec refers to the dimensions of the thermistor, which is 0.04 x 0.02 inches in size. Lastly, ROHS (Restriction of Hazardous Substances) refers to the fact that this component is compliant with environmental regulations for hazardous materials.