It looks like it could possibly be the remains of an early Harvey-Wilcox livestock marker (ear tag), originally patented August 8, 1899, and used up throughout the first part of the 20th century.
I'm not for sure of the proper name. I've seen button that look similar to this from the 1700s that were refered to as nipple buttons because of the raised center
I'm not for sure of the proper name. I've seen button that look similar to this from the 1700s that were refered to as nipple buttons because of the raised center