I thought this may be part of a timed fuse but I'm not sure. I guess that is a 6 on it. It is about an inch long and rang up well on my detector. I found it on a hill that was shelled during the war. Also found several pieces to artillery shells that day.
Your guess is a good one. Specifically, your find is the "lip" of a (yankee) Schenkl Combination Time And Percussion (impact detonation) artillery shell fuze. It was used almost only in nothing but Shenkl Case-Shot shells, with just a couple of known exceptions turning up in Parrott shells.
Here's a couple of photos for you, one showing all of the time-markings (the fuze's rotator-cap is missing), and the other showing the fuze entirely complete.
If you found it in the same area where you found your unknown frag, it adds weight to my tentative guess that the frag is from a Schenkl Case-Shot shell.