We spent hundreds of hours developing our Classic Leg Vise, which includes lots of time researching historic forms.
Most of our research takes the form of hunting down early photographs, which appear in everything from vintage tool catalogs to postcards. We also keep our eye out for ancient workbenches in modern contexts, like Ebay, auction catalogs, and lifestyle magazines. The latter is our favorite source, purely for the entertainment factor. Our image collection of bastardized benches is enough to make any woodworker cringe.
But now and then we stumble on a real gem, like the picture above from a school for disabled veterans.
One thing we found interesting. It seems shortly after Roubo's time, and the advance of the industrial revolution, that at least in France (and its colonies in North Africa like Algeria and Tunisia) the vast majority of extant benches featured metal vise screws, not wood. Why fewer wood screws? I think in a school or commercial setting, the metal screws were probably viewed as more durable, and with mass production coming into play, they could be made quickly and cheaply.
French leg vise screws invariably feature a metal hub and handle. English and American versions almost always use a cast "T" with sliding wood handle. We chose the French version to allow our handle to center up repeatably and reliably (this is nearly impossible with wood) and also because the cast "T" version is already available from other tool makers such as Lie-Nielsen.
We've uploaded some of our research images here.