I saw someone else was making a replica of this chair and got to wondering how the hardware actually worked.
Short version I'm wondering what else this kind of hardware would be used for and where you might find it. The basic design appears to be a pivot on each end of a short brass (plated?) arm that's strong enough to support a persons weight.
My searches thus far for the obvious verbiage haven't yielded anything useful yet.
Here's the somewhat longer version with some more pictures and links.
The inspiration is this fellow teaching a class on chair weaving:
He seems to have some very nice quality hardware on that chair with a smooth topped surface
Relevant picture saved here for posterity.
I see some other replica's that use less spiffy hardware but have a couple of nice pictures of how the geometry works
Pictures again added locally for posterity.