Based on my research, I believe that I have a pair of Finn Juhl 138 lounge chairs. They both have the round France & Sons metal stamp.
My questions relates to the method in which the backrest is attached to the chair frame.
On my chairs, there is a small pin that screws directly into the side of the back rest to support it to the main frame (second photo).
On other chairs that i've seen, there is simply a large visible bracket that screws into the rear of the backrest (last photo).
Does anyone know why there are two different designs? What is the original design?
thanks! 
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I think the answer is they are both the original design. The model 138 is well documented with both variations of backrest connection.
I had a sofa version with the former mentioned metal rod connection which if I remember correctly was a later production by France & son (up to 1966).
Perhaps the earlier chairs had the different connection?
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