ID - eames fiberglass armchair with bolts in base?  

no-go
just to clarify:
I'm leaning toward thinking that this chair is NOT an original. I wanted to confirm with the forum, or perhaps be pleasantly surprised to hear that maybe it's something rare.

Some (if not all?) of the...
Some (if not all?) of the upholstered fiberglass shells don't have shock mounts. They have bolts that screw directly into the underside of the shell. The other side of the screw holes are hidden by the upholstery (vinyl or fabric). Is it possible this is an authentic shell with the upholstery taken off?

Later
Later upholstered shells did not use shock mounts. The shell itself was directly tapped. It's curious that the shell in question has no stamp or mark. Perhaps pics would be helpful.

Coming out of the shell
Thanks for your comments so far. Yes, I knew that this was how upholstered shells worked, and was on the look-out for that.
No, this one actually has bolts that are embedded into the bottom of the fiberglass shell so that the threads are sticking down.
I don't have any pictures on hand, but the form matches the HM examples pretty well, with this major exception of underside mounting.
Would love to hear how this influences your responses.

Carnac The Magnificent says...
Carnac The Magnificent says "it is fake."
"But without a picture, who the hell knows."

Pics would really help
HM shells did not use a mounting system that you describe so it's probably a knock-off or has been altered.

Thanks!
That's all very helpful. Thank you all so much. I really appreciate it. Now I know. next time I'll snap some good pictures.

Krueger shells, which look...
Krueger shells, which look similar to HM shells, have screws/bolts that come directly out of the bottom of the chair. They are generally marked as Krueger Metal Products and include Green bay Wisconsin as their origin. Krueger chairs are commonly mistaken for HM by many people not familiar with their differences, but if you look at the two side by side you will notice obvious things like the shape of the top of the shell is more squared on a Krueger and the bolts/screws under the chairs are almost always directly attached to the fiberglass.
Hard to say for sure without a picture, but my guess is that your chairs are Kruegers based on the descriptions above.