A bomb.
No shit. At least I think it is a bomb. There was an old army firing range near my parents house. After a hard rain, you could go there and find spent shells, mushroomed bullets and sometimes if lucky some of these bomby thing shaped cone heads.
It is about the size of a softball, but a cone shape, rounded on top. There are "layers" about 4 deep going from head to base, each layer has a set of numbers on it with a little "knob" or head that you can twist to rotate the marker to specific numbers based on whatever they mean. Atleast you could then, by the time I found them, they were rusted, impacted too much to turn.
you turn it over and the bottom 1/3 is a hollow with a indention and thread type on the bottom so you can screw it on to whatever.
hard to explain... I will have to take a picture next time. Or if this sounds familiar to any of you army buffs, can you find a pic online to link to and I will ID it.