kcombs,
That's a drum puller for older cars where you had to remove a cotter pin, a nut & a washer. Then you installed the puller with the 3 arms & used the lug nuts to hold them to the drum. You wound it up until the center part touched the axle & with a BMFH (a big Mother Fkin hammer) you wacked the leg until the drum popped from the axle.
It was used on MANY old cars. I still have mine I bought in the very early 60's. They take a beating that's for sure. No China stuff would hold up today to the beating it takes to remove some of those drums.
Tom T.