Hi Jon,
It's an ox horn tip. They were screwed onto the tips of oxen horns to keep them from goring things. The small hole was for a set screw. I'm betting the larger, threaded hole in yours is tapered, no? Sometimes they are and sometimes not. We find them all over New England - and I have so many that I've got a coffee can dedicated to just them. You'll find them in all different sizes - some faceted for use with a wrench, and some just round balls. Not to be confused with lug nuts - which wouldn't have a set screw - and wouldn't be tapered. Oxen weren't used much later than the 19th century - so it's probably from that era, though I have run across a farmer who remembers them from his youth.
Hope that helps. -Dan