Great examples of three variations of the #1 pruner you have there Vit. On top is the most recent of the three, which appears to be outfitted with Delrin handles. DuPont completed construction of a plant to produce their own formulation of acetal resin, calling it Delrin, in 1960. The middle knife is the oldest, judging by the 4-line tang stamp. Note the absence of a brass liner lock, which is indicative of knives manufactured during wartime, when most brass produced was used in the production of arms. Since the 4-line tang stamp was used from '41 to '46 and the second world war lasted from '39 to '45, I would question your dating of that knife "PRE WWII" (pre 1939) there Vit, but I could be wrong. I'd say the bottom knife was indeed produced in the late 1940's to early 1950's as you indicate Vic, judging by the tang stamp, wooden handles and brass liner lock.
