since i am the odd one out...i will say i believe it is closer to vietnam then WWI.
most of the WWI bras i have seen is solid, screw back post...i have seen some WWII collar brass that was hollow, pin back...but this one looks like it has fire damage and could be a later piece.
Thanks guys for your answers, I had a little time this morning to do some research after Crusader got me going in the right direction, I found one on a 1917 uniform that was pretty close but not an exact match. I'll look closer to Vietnam era as well.