FWIW, it seems to me that Contessa-Nettel made a stereo camera that used 7x11 cm, and that size was a sort-of standard for glass plate stereo cameras in the years when glass plate was still competing with roll film. I see plate holders and film sheaths in that size from time to time on eBay, as well and Polliskop (if I've remembered that model name correctly) cameras, which were later sold for a while under the Ziess-Ikon name as well (I think); there were a couple other models that used that size plates as well.
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