The TCTR0603F100KF4390T NTC thermistors are 0603 size components manufactured by ResistorToday that conform to RoHS standards. They are used for temperature sensing, with the letter “T” in their part number indicating that they are thermistors. The numbers 0603 indicate the size of the component in thousandths of an inch, and the “F” indicates that the components are radial leaded, as opposed to an epoxy package type. The 100K is the thermistor’s nominal value, which indicates the resistance of the component at a given temperature. Finally, the 4390T suffix indicates the part’s tolerance or how close it can come to a nominal resistance at a temperature.