Well, I'm still learning this machinist stuff, but I'm sure I have one of those chucks, too. It came with an early 12" Craftsman metal lathe. I'm still trying to find a dataplate with no luck, but I am sure mine is from the mid or early 1930's. My chuck has a hole in the body that is similar to the holes in the edge of the scroll. From what I see, you stick a Tommy bar in the single body hole and a Tommy bar in the appropriate hole in the scroll and move the bars in opposite directions to loosen or tighten the jaws. Could it be a Sherline chuck? My lathe has some differences that I first thought were repairs or adaptations, as they are not on any of the early Craftsmans that are pictured on lathe websites. But these differences are on some drawings and pictures of early Atlas 10" lathes. jrh