This piece of equipment is used to wind and measure a skein of yarn. One end of the yarn is tied to one of the arms and then it is turned to wind the yarn around the other arms. There are wooden gears inside the box to which the axle is attached. After a certain number of revolutions, the gears will cause a thin piece of wood to slip and produce a loud "pop" or "click". When it pops, you know how many yards you have wound at that point.
I have used several antique weasels over the years and they all pop at a different measurements, so it was evidently up to the maker to decide the length of a skein!
I have heard this item referred to by several different names: skein winder, clock reel, click reel, and a weasel. WAIT A MINUTE! Weasel? Yep! When I was first introduced to this piece of fiber equipment by an elder lady, I was told that it was called a "weasel." Hmmm...weasel. I have also heard that this is one explanation for the song, "Pop, Goes the Weasel".
For a more detailed explanation and some nice photos of the wooden gears inside click here.