ID REQUEST: Herman Miller / Eames stackable fiberglass chair  

Hi 🙂

I'm hoping someone can help me identify whether or not this is an original / authentic Herman Miller - it was a spontaneous consignment shop purchase under the assumption that it wasn't the real deal, and the legs are not in the greatest shape... but upon closer inspection, the body does seem to be fiberglass and the marks on the underside are there. Thought it wouldn't hurt to ask! Thanks!

(Not sure why the images posted sideways like that, sorry!)
<img class="wpforoimg" src=" http://d1t1u890k7d3ys.cloudfront.net/cdn/farfuture/6ym2VS-MPGvvmkMNlvLAwg