the knive photos do'nt show the base of tang
my initial observation may be incorrect
on my knife which could be over 100 yrs. old
back of tang is notched ; when lever on top of spring is pushed up the blade is unlocked
essentially letting lever down locks the blade in position where it rests at that moment
so blade is locked open or closed & any other position when lever is not actvitiated .if closed & lever is held up momentary, & THEN BLADE IS OPENED rapidily lever lock , when released floats as the rapid opening keeps it from locking ,till open
the quick open makes a noticable clicking noise
these type knives were the real early tactical folders of the day
stiill produced & common in spain,port.& some in argentina. i've seen a few from 1800s with absolutely beatiful etch scenes on blades.all the ones i've seen were old ,forged,great fit. blades are fairly wide though thin ;
gives them strength in a light blade.