Pyrex ground glass stopper

I have an assortment of vintage glass reagent bottles I'm preparing to sell, and I need to know how to describe them accurately. Some have "pennyhead" stoppers, some have "flathead stoppers," and some have "dropper stoppers," but I'm stuck on what to call a fourth type of stopper, which is only on the Pyrex bottles. They look like this one:

http://www.ebay.com/itm/Pyrex-24-Gro...-/120596121368

Does anyone know if this type of stopper has a name?

Stay tuned! Let me get an expert on this!

I've always referred to these as "Thumb twist" or "Flange" stoppers, but have not seen very many of them referred to in any way other than just "Stopper".