The 4-size watches are noted from several sources, including the 1913 Trade List and Chris Bailey's interview with Wesley Billings, an employee at the factory from 1911 onward. There is no known model number, but they were offered in two grades as part the Centennial line as a factory-cased pocket watch. The problem is that this model, while open-face and pendant-set, measures 34.65 mm in diameter, which is a standard 6-size movement. Billings stated that at the time there were a total of 23 models, which have all been accounted for, so if a true 33.0 mm 4-size was indeed manufactured none have been reported yet. It's also very unlikely that the company would tool up to make a third 6-size model, so the simpler explanation is that they continued production of a variant of the Model 18, sold in snug cases and marketed specifically as a girls/ladies' watch.
* This is an assigned model number. The factory designation is not known.
Roughly 50,000 were produced in a single uninterrupted run, with all of the reported examples falling between SNs 3,053,000 and 3,103,000. Several named grades have been reported, but no private labels and no two-tone plate finishes.
The only known grade assignment was in the 1913 catalog, where the Grades 320 and 322 were labelled as 6-size movements. They were listed along with the 12-size Model 22 and 16-size Model 21, the other two watches making up the Centennial line, which is another reason to think this may be the advertised 4-size watch. Whatever their real size, they were included in the 1914 Supplement, the last known pocket watch catalog.
There were only two known grades offered in a nickel pinstripe pattern, identical except for the jewel counts.
According to both the 1913 catalog and the Billings interview, the Centennial Series was made in only the three sizes of 4, 12, and 16, with no mention of any 6-size watches. Either the company was marketing the 6-size Model 24 as a 4-size watch in a very small factory case, or there really is a 4-size model, which hasn't been reported yet.
The company offered a larger 4-size wristwatch, and the only known ad cut (repeated in several jobber and trade catalogs) shows a configuration of a pendant-set open-face watch, the same layout of the Model 24, which has already been established as a 6-size watch.
Why Seth Thomas chose to carry a second wristwatch with the clumsy arrangement of the stem at the 12:00 position is not clear, but given the difference of 5 millimeters between this watch and a 0-size it's no wonder the ad text includes the disclaimer that the 4-size case was "a trifle larger".
There were plenty of named grades to accompany the factory-numbered ones.
Click here for the entire alphabetical list, along with models and jewel counts.