Vendors will continually call these C Mount unless they have been corrected.

weirdstuff-inc an eBay vendor, sold me 2 NOS Cosmicar 50mm f1.4 lenses, with 46mm pl filters, as C-Mount.

I have given him the bad news. As I am in Oz and he is in the USSA, no refunds are likely. He is otherwise a good vendor!

Perhaps this thread will fill up, making it more difficult for mistakes to be made?

Still may be worth buying, if you like vivisection!