Vest Pocket [Model 420] © 1938 Mills Novelty Co.
3-reel miniature bell.
Model 420 is the first Vest Pocket release. Certainly the smallest slot machine made.
Collector's Guide to Vintage Coin Machines - Richard M. Bueschel - Page 53
The Coin Machine Journal - January 1940 issue
Loose Change Blue Book for Slot Machines [4th Edition]