This one's new to me. No luck trying to find it. Roughly 2.5" height and 2.75" width. No markings anywhere which makes me think they were possibly on part that was removed. Any help would be greatly appreciated. 

It is a U.S. Mk VI Fuze for Stokes Mortar

I'm taking a guess but I think this is for a WWI ear Stokes mortar.

Possibly a Mk 4 or Mk 6 fuze.

I have a Stokes mortar that is a field pickup with heavy pitting and no fuze. I don't think these fuzes are all that common.

edit: the above post with pics came in while I was typing my reply. I'm happy to not have been completely wrong. ;-)

 

Thank you for the help. As always lots of knowledge here.