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The long bolt is a socket head cap screw. I find McMaster Carr to be an excellent resource:
http://www.mcmaster.com/#socket-head-cap-screws/=x1cf8d
You can find them in almost any size and material there.
Is the other component threaded? Or is it simply a flange to provide a pocket for the head of the cap screw? It may be a custom component unique to Hans Wegner.
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