It is definitely a civil war artillery shell's "impact-detonation" fuze. At the time, such fuzes were usually called a Percussion fuze. The one you found was designed and patented by John P. Schenkl. Thus, it bears his name (and the US patent-date) on its face. Strictly a yankee-made fuze, by the way.
Congratulations! If the whole thing is as undamaged as it looks in your photo, it would retail at a civil war relic show for about $75 to $95. You may see these patent-marked Schenkl fuzes priced higher elsewhere, but I'm talking about how many dollar bills change hands, not "the sticker price." ;-)