A very early Waterman lever-filler

This pen is one of the earliest Waterman lever-fillers I have yet seen. Early PSF-series lever-fillers have the narrow raised barrel threads, but much less common is the form of the lever, shown below, stamped of thinner metal than later examples, with a small end with a narrow margin around the globe logo imprint, and plated rather than gold filled.

The recess for the lever end is also distinctive, and also rather crude compared to later examples. It is flat-bottomed and appears to have been made by milling a simple oblong depression -- basically just two overlapping circular recesses.

Early Waterman lever-fillers with the raised threads normally also have a sprung two-piece pressure bar, as shown below. The J-shaped spring has a T-shaped end, which toggles into a slot in the rigid pressure bar. Unlike later pressure bars, this bar is not toggled to the end of the lever, and the matching lever lacks the necessary tabs or "ears" to engage a later pressure bar.

This pen, however, has an even more unusual pressure bar. It too is two-piece and sprung, but here the spring has a C-shaped base to hold it in the barrel, and its other end is permanently attached to the rigid pressure bar by a single rivet.

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UPDATE:
Here is a better close-up of the lever box area, which also shows another very early feature: the bent-over tab that serves as a lever stop, rather than the solid crossbar that is seen on all later Waterman lever boxes. At the bottom is a comparison shot of another early PSF with raised threads and sprung two-piece pressure bar, but with the more familiar lever box construction and fingernail groove in the lever end recess.