Zenith Eames side chair?  

I picked this shell up over the weekend and was interested if anyone could give me more information. I tried searching past threads and found a lot of great information but just could not seam to find an answer on this stamp. I picked this up in a store in Texas and it was among a stack of 12 or so shells but none of them had bases anymore so I am not sure what was originally on it. It has no embossing or Herman Miller logos on it but it does have a silver stamp on it that I believe reads "Zenith 3 Prime". It also has some numbers stamped below. Can anyone tell me anymore info?
<img class="wpforo-defaul