There now having been two guesses that this object is a munitions (artillery, grenade, etc) fuze, eventually somebody is going to ask me about it. So, I'll go ahead and speak up now to say it is definitely not a fuze, nor a fuze-part.
I've seen one before, but I cannot recall where I saw it sometime in the past 50 years or so. (It's frustrating that when you get into your 60s that although the light is still on in the attic, some cobwebs are definitely forming in unused corners.)
The object's finder (Bbuddy) says it is "a little larger than a quarter." A sideview photo would be helpful, so we can see if it has any threading or other way of attaching it to something.