Are they vintage? As far as I know, the only mfgr that made 7/16-inch drive tools is Blackhawk, from the 40s (except WWII) through the 50s or so. They marketed them as an economical alternative to owning 3/8- and 1/2-inch drive. Branded as Nuggets. Not rare. Not growing on trees, but not rare, either. The concept did not last and did not, as far as I know, spread to S-K or any other mfgr. I could be wrong. I don't know much about modern tools, if you're talking about some modern retro trend. But if you're talking vintage, maybe they're Blackhawk in an S-K box?