For those of you who knit, you're likely laughing right now. For the rest of us, this piece of metal equipment is a yarn winder. It's purpose is to enable you to easily wrap your yarn into balls, which I'm told makes it easier to use. Once the yarn was wrapped around the legs of this machine, it was attached to a bobbin, you turned a hand crank, and your yarn was turned into nice, neat, no-tangle balls. The picture on the right shows what it looks like once the yarn is wrapped around the legs.
This one is approximately 23.5cm in diameter and 13.5cm high. You can adjust the size of how big you want your skein (ball) to be by loosening the wing nut (shown below) and sliding the arms closer together.
Some are large enough to be floor models but this particular one is portable with a "C" clamp base to attach it to a table. It's solid metal and there is no washer under the wingnut. Although there is no date or brand name on this machine, the patent for wingnuts first showed up in 1933 so it's origins are early to mid 20th century. Yarn winders come in all different sizes and materials. Some are made of wood, some like this one are metal, and of course many modern day ones are plastic.
It's always interesting to find artifacts that, although almost 100 years old, are still very similar to today's technology. (1968.174)