The brass thing is a clasp for a bag...a hole in the flap goes over the brass thing and the top of the brass thing turns to lock. Must be a more official name than brass thing?? Probably used on a uniform bag or saddle bag.
Thanks for the update, and the Half dime is at home, and I'm at Lisa's, won't be home till tommorow but will check the mint mark and post it here asap.