Found this at a flea, seems to hold a round shank ok.  Any other uses or a proper name?

Quote from: john k on December 01, 2020, 01:58:10 PM...a proper name?

Well, the proper name for "chuck" would be "Charles," of course; but that's prolly not what you meant.

I've never seen anything quite like that.  Another genius idea that went nowhere, I guess.

What does the end look like? Any markings on it?

Well, obviously it is designed to fit a brace, so it is a "brace tool".  Jokes aside, someone's idea of a different type of chuck.

Hard to tell without seeing the business end!! Maybe a chuck  for dies??

Business end

Looks like the set screws may be for holding cutters? Perhaps some sort of cylinder hone?

maybe a ridge reamer for cylinder walls?

The screws are geared together pushing the jaws in and out.  They are driven by a female square on one end.  Like a chuck key.  I would dsassemble it to show the pieces, but it  doesnt want to come apart.   I think I have another chuck similar to this but much larger, but it seems to be hiding in my old shop.  Whenever a tapered shank item, or drill press piece surfaces it comes home with me, provided the price is low.

Quote from: john k on December 03, 2020, 01:08:45 PMWhenever a tapered shank item...surfaces it comes home with me, provided the price is low.

It is amazing the range of items that used to be chucked in braces (and breast drills, which were available with tapered-shank chucks, actually a better chuck design for a heavy-duty drill like a breast drill than a hand-tightened three-jaw chuck).  I recall asking an auto shop instructor once why no one was making (then) an adapter to fit braces, so you could use them like a speed wrench; his reaction was, in essence, "braces are carpenter's things."  I now know that he had no idea of the history of his trade, since a lot of automotive tools were made to fit braces.  I've got a valve-lapping tool for a brace, for the older valve designs that had two holes in the face of the valve for two pins on the tool that turned the head around to lap it to the seat.

They made brace wrenches for braces with a 4-sided tang to turn them into speed wrenches.  I have about 50 of them by different makers including a full set by Billings.

It reminds me of a Jacobs style tap chuck that has a clamp system similar to that to capture the square heads on taps. It also has a lower chuck section that captures the body of the tap.