George Nelson?  

I
would assume the fitting maybe takes another stool leg to form a line- for a school perhaps?

Maybe
every other stool had a hook?
Sort of male & female.
I'm just guessing.

Here's a better photo
of that detail. It is rectangular, so I don't see how another stool leg would fit into it?

Its a Tony Paul table. The...
Its a Tony Paul table. The part on the leg is to hold the missing piece -- a cup holder

it might be a plant stand
I have the same thing for years and it seems to work well as a plant stand sitting comfortably next to my 'antelope chair' by Ernest Race.

sounds
like a lovely match!

Thanks Parofo
Cool, good to know. I don't mind living with it the way it is.

Tony Paul
Tempo series.
http://www.tonypauldesigns.com/blog/?page_id=115

Good example
parafo and woodywood are correct of course, but this is a great example of how incorrect attributions spread on line. If diors had not asked for feedback and had they been a dealer or eBayer who advertised the table as a Nelson design (it's easy to see how one could make the connection between the ball clock and this table) one can imagine how others would have used that attribution as well. Especially if the table had bought a strong price. Others follow suit, and before you know it, a misattribution is more commonplace than the correct one.
The Tony Paul designs are reasonably well known, so diors' question was answered quickly. But if a design is more obscure or harder to document, it's not surprising how incorrect or questionable attributions spread.
By the way, I really like Tony Paul's work and that is a great little occasional table. Fix up that top and you have a wonderful, useful little piece.