For use with 14 watt, 15-inch tubes, 15 watt, 18-inch tubes and 20 watt, 24-inch tubes. Fluorescent starters are used to help the lamp light and to not flicker. Replacing a starter is recommended if tube is not completely lit or tube continues to flicker. If the tube is discolored on the ends, then replace the tube. Each starter measures 1 1 / 2 inch L x 3 / 4 inch in diameter.