It made its debut in 1937 and was produced until late in 1942 when. The Mills factory in Chicago converted to wartime production and stopped making slot machines until the war ended in 1945.
The idea behind the bonus feature was to entice the player with a chance to build up letters and win an 18 coin payout when the word BONUS was completed. The letters that spell B-O-N-U-S are superimposed over the regular fruit symbols on the first (far left) reel. When the reel stops on one of the letters, that letter will be added to the top bonus display on the top of the machine.The catch is that the letters of the word BONUS must be spelled in sequence in order to advance. In other words, if the player has B-O-N- appearing in the bonus display, he needs to hit a U to advance a letter on the display. If the player hits an S, it will not score until he hits a U first. The machine pays out 18 coins when BONUS is completed and with the next coin deposited the display will reset and remains blank until a B is hit etc. Launched it's first mechanical upright cabinet slot machine in 1897. I can provide more photos upon request. Contact me with any questions. The item "1938 Mills (Bonus Bell) Horse Head 5-Cent Slot Machine (Completely Restored)" is in sale since Friday, February 8, 2019. This item is in the category "Collectibles\Casino\Slots\Machines\Antique Coin Slot Machines".
The seller is "nimslot60" and is located in Yuba City, California. This item can be shipped to United States.