This shell is distinctive type: It is noteable for
what is not present: no embossed "Herman Miller" name or logo, and no extra flattened
places to accommodate the spider or stacking bases.
It has a self-leveling glide, made of black rubber and metal.
The Herman Miller catalog reports that in 1957 white nylon self-leveling glides were introduced, eventually replacing these. It may be that they had some of the previous glides left over, when they put this chair together.