Hello again Bombgod1. Thank you for your kind words about my book. Having been a relic-digger for over 30 years, I'm certain that what you've found isn't technically a button ...it's the "collar" part of a overalls-rivet (in this case, a Railroad Worker's overalls). It's what the over-the-shoulders straps fasten to, on the top front of the overalls. In case you've never seen what I'm talking about, a very similar collared-rivet is located above the zipper on most blue-jeans. A rivet is used because a button (attached by thread) isn't strong enough to hold the two pieces of jeans-fabric together. Because rivets of this type have been in use from before the civil war up to today, there's no way to be certain how old your item is.
Regards,
TheCannonballGuy (PCGeorge)