Motor start capacitors temporarily store an electrical charge to deliver extra torque (where torque is the measure of a rotational or twisting force) during motor startup. They exit the circuit once the motor reaches its operating speed, unlike run capacitors, which help maintain a motor's running performance. Motor capacitors are primarily distinguished by their capacitance value, which is measured in microfarads (mfd or µF). When replacing a start capacitor, it's important to match the microfarad rating, voltage, and dimensions to the original capacitor. Start capacitors work with motor designs designated as capacitor-start or capacitor-start/run, and they are typically used with motors that power fans, blowers, and pumps.