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					Originally Posted by ingelred
					
				 Hello, 
 I just took a look into NAVAJAS ANTIGUAS - ANTIQUE CLASP KNIVES by Rafael Martinez del Peral y Forton.
 In picture 018 on page 19 You can see a Navaja very similar to the Navaja shown in style as well in the detail of being a slip joint (it's the one on the right).
 The book says 19th century Albacete.
 
 Greetings, Helge
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 G'day Helge,
Please do show the image you refer to, I am interested as I have never bought the book, only the knives.
I too cannot see any ratchet teeth but ratchet lock or slip joint, a back spring is a spring that sits on the back of a knife and both ratchet or slip joints mechanisms do have a back spring that is clearly missing on this piece.
 
Look to the out of place circle to the middle, it is a pin to hold the back spring and the empty hole towards the rear of the handle, is where a pin would sit to hold the rear as seen in both slip joint and ratchet mechanism back springs.
 
As a footnote 

  I know I have one Alvero Garcia exhibition Navaja here that has proved Forton wrong on one count on manufacture. 
 
 
Well noted about the slip joint though.
Gav