Congrats on the start of your year.
The last piece is interesting but its robust fixing pins rules out Medieval (I believe). The Pins look to be 18th-19th C. Its odd, because if it were meant to go on leather its been over engineered. Maybe it gave strength to a joining point of 2 leather pieces? It's interesting & although it probably was on leather, I wonder if it had another function.
PS. Might be Brass.
Wow, those are some productive fields! Where are you located (country)? Love the finds, and thanks for sharing.