Link to David Nishimura'a Vintage Pens about Waterman's lever filler with illustrations.
The earliest Waterman lever-fillers have a number of distinguishing features, including narrow raised barrel threads and a two-piece pressure bar consisting of a rigid bar attached to a spring. The end of the lever which bears upon the bar is rounded, and does not link the lever to the bar.
https://www.vintagepens.com/images/perm/Waterman_PSF_mech.jpg
https://www.vintagepens.com/Waterman_lever-fillers.shtml
(c) David Nishimura's Vintage Pens
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