Posted By:
HankronI add that, just like AA and AAA batteries and size 9 and 10 shoes, the various names for the size of the mount ('cabinet card', 'CDV' and many others) were commercially standardized by their dimensions. Various national and internation companies manufactured cardboard mounts and sold them to photography studios. One can find (including on my site), long lists of standard sizes and their names. Names include 'promenade card', 'Swiss card,' 'Boudior card' and so on. There are so many names, one shouldn't even try to memorize them. As I meantioned earlier, when in doubt call one a 'card photograph' or 'photograph card' and give the measurement.
Cabinet cards and cartes de visite (aka CDVs) are the most commonly found and heard of.