These interesting and unmarked chairs are really solid.
Very similar to those pictured in Seth Peterson Cottage (see last picture). https://franklloydwrightsites.com/wisconsin/seth_peterson/seth_peterson.html
Possibly these chairs were prototype for the 'Form' chairs used in Chipotle restaurants.
Note that the second last photo in series here is of an actual FLW chair for comparison (taken from an online source)...and is not part of this set!
This information from Steve Sauer might also be relevant regarding the restaurant chair idea: http://www.oixio.com/habitat-solutions/form/form-chair.html
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