A recent post of mine ("High Jeweled Waltham O Size".) got me thinking about Waltham’s first 0-size watches. Their first 0-size movement, the 1887 model, was a modification of their 1882-model 1-size movement. In the photo below the 0-size is on the right. The principal modification was just trimming the plate and bridge diameter, but they also moved the case screw and added a second case screw at the balance cock. These were positive setting and used a detent stem and had one plate covering the entire train and barrel. A major change was initiated with the 1891-model, which was a negative setting movement with a split-plate design to make casing and assembly easier. Waltham was evidently experimenting with winding/setting mechanisms at this time, and the 1891-model exemplified this with two fundamentally different setting mechanisms, and with at least two variants of each. (The same mechanisms were also used in their 6-size 1890-model). The changes in setting mechanisms also coincided with a series of small changes in the plates of the watch and a few other features that I will describe in this post. I previously noted three different configurations (Another uncommon Waltham 0-size) but now can define five versions, which I will differentiate as models 1891-a, -b, -c, -d & -e. To explore the progression of movement details, I can use cuts conveniently provided in the 1898 S.F. Meyers Co. catalog (reproduced by Roy Ehrhardt in his 1974 “American Pocket Watch Identification and Price Guide, Book 2”). Please note the bridge shapes and screw locations; other finish details are grade-related and not relevant to the plate styles. Descriptions are supplemented by observation of actual movements. 1891-a This was the first plate pattern, which appears to have been used for the first couple of years. It is notable for using a pallet cock for the pallet fork. The small train bridge was held by only one plate screw (not counting the case screw). 1891-b This second version switched to a small bridge for the pallet fork and a second plate screw was added to the train bridge. 1891-c The third version saw a plate reconfiguration. The train bridge was enlarged and the barrel bridge was reduced in size, but the plate screws stayed in the same location. This version appears to have been rather short-lived and, so far, I have only seen it in the first run of Riverside Maximus grade movements. 1891-d The fourth variant, with a new location for the second train bridge screw (moved closer to the barrel bridge), quickly superseded the previous version, and was otherwise the same (other than changes in the setting mechanism, described in the second post). The movement serial number for these first four variants is on the barrel bridge. They also used small dial screws that entered the edge of the pillar plate at an angle and locked the dial foot with the tip of the screw. The next (fifth) version used a different dial screw with a larger head that impinged on and locked the dial foot in place rather than using the tip of the screw to do so. 1891-e The fifth version uses the same plate configuration as 1891-d but introduced a few minor changes, such as the new dial screw as described above, and the movement serial number was moved to the train bridge.