Depending on how large it is I think it's part of a wagon suspension. Called a "Shaft Box" or "Shaft Coupling" it attaches the axle to the frame that held the box and seats.
Size would sure help to get a better definition. Right now only you know how large it is.
It was something which was attached to wood for some reason. The wood has long disappeared. Could be from a wagon or any number of things. A farm implement, a gate, who knows?