The Model 20*


1908 to 1913

The Model 20 was the company's only known 0-size movement, measuring just a little over an inch in diameter. ​​​It was a bold move for Seth Thomas, with the popularity of wristwatches on the rise but peaking well after WWI. They first arrived in the 1908 catalog, offered in three jewel choices in only a stem-set hunting configuration as an uncased movement or as a wristwatch with a factory-supplied leather strap.

*  This is an assigned model number. The factory designation is not known.

Jewel Count and Grade

The Serial Number Blocks

5,000 Total

The Model 20 was evidently made in a single unbroken run of about 5,000 watches. All of the reported examples are between SNs 2,000,001 and 2,004,800, with several movements having no serial number.  All Model 20s were made in hunting configuration with a choice of two dial layouts to place the stem at 3 or 12. 


The Production Dates

1908 to 1913

 The 0-size Grades 1, 3, and 9 first appeared in the 1908 catalog and continued in all of the known catalogs until the end of production in 1913, with prices of all the grades doubling by the end of their run.

The Model 20 Chart

The watches logged in the M20 chart are all reported examples or verified from photos.

If your watch isn't on this SN chart please send us a picture.

Seth Thomas M20 Database (pdf)


The 1908 Parts Catalog


The Grade Chart


There were only three known grades; all nickel-plated and hunting but with different jewel counts. 

The 0-Size Wristwatches

The Model 20 was offered as a wristwatch with a choice of straps or an uncased open-face watch, because none of the period company adverts actually listed a 0-size nickel or gold-filled pocket watch case. The factory wristwatch case was nickel, with a black Morocco or pig skin strap, selling for $14 in 1908.