Arthur Umanoff Chairs?  

I think
the legs should be solid metal, right? Not tube metal? Do all Umanoff stools rotate? I don't know but the only one's I have seen did.

No, all Umanoff stools do...
No, all Umanoff stools do not rotate, infact Ive seen more stationary ones than rotating.
There are a plethora of variations on these stools that mix and match components.

Thanks...
They do swivel 360...
Thanks...
They do swivel 360 degrees. The metal is all solid, no tubes. Screws are slot screws. The ends of the legs have self leveling white plastic caps that look vintage, but don't seem to go with the design of the chairs.

well
the only set I have seen that was for sure Arthur U had those attributes. All of the knock offs I have seen have had tubular steel and I THINK have all been non-swiveling. Not an expert on these...

Weird, I have never seen a...
Weird, I have never seen a single Umanoff-styled chair with a tubular base.
Ive come across atleast 30 of these over the last couple years in various forms, some standard chair height, some stool height both nonswilveling and swiveling, lounge style and dining style.
All of them shared a solid metal base, same wooden slats, plastic glides, fasteners and screws. The white glides are not original.