I found 5 of these at a local flea market....they look like Risoms and they most defintly are old....but they seem like some kind of vintage knockoff to me....what say u guyz? Bottom is marked model 466, one of them has 466 hand written, and I am pretty sure on the bottom of the one pictured faintly above the middle 6 you can see "occupied Japan" ?(8^( ? 
<img class="wpforo-default-image-attachment wpforoimg" src=" http://old.designaddict.com/sites/default/files/forum/photo4-3. 
The under seat construction...
The under seat construction details look a bit crude and do not look like Risom to me. However, the overall chair design is somewhat interesting; kind of a blend between Risom, Carlo di Carli, and Heywood Wakefield . . .probably the first time those three have been mentioned in the same sentence.
not risom but in the style of
the risom model 666 chairs (all variations) have straight back seat rail not curving like your chair. the upholstery would have wrapped all the back rails not screwed and plugged like the one you have and also knoll would not have imported the risom chairs from 'occupied japan' (that is equivalent to made in china today/made in hong kong or taiwan in the 1970's and 80's.
even though mass produced and not so bad knock off, you have a decent well made chair compared to the heavily marked up retail furniture that you will buy today.
it is not valuble so this is a good opportunity to play with the wood finish and upholstery (or webbing) if there's a need for it.
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