That is what is call a whatsit. It has many uses, it weights 22 lbs. It can be used to hold the corner of a tarp down when it is windy. I have seen it used on a bull to keep it from running(you may not want to know where it was tied or be the person that did the tieing). Back in the day it was used to crack black walnuts hence the black color. and it was used to test the breaking point of toes to determine the gage of steel to use in steel toed shoes.
But these are all guess's